News, comment and latest developments in wind tunnels and aerodynamic research and development 2009 ANNUAL REVIEW
1000 mph – on land Low-drag golf club America’s Cup secrets Aerodynamic trucks Heading for Mars CFD comes of age
Inside BMW’s Fabulous Aero Test Center
Optimised wind turbines
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l www.mts.com email@example.com Tel: +1.952.937.4000 Mts ground Vehicle solutions ©2009 MTS Systems Corporation. MTS is a registered trademark of MTS Systems Corporation. RTM No. 211177.
14 05 WELCOME
When did you discover aerodynamics? Did it involve a hand and a car window?
06 NEWS The latest from the world of tunnels. From zoomy to zany…
14 FEATURE: BMW ATC Nothing more advanced in autos. We go deep behind the scenes
20 FEATURE: INSIDE VIEW How the ATC fits in BMW’s R&D. Q&A with BMW Aero Chief Hans Kerschbaum
22 FEATURE: 1000 MPH – ON LAND Bloodhound SSC aims for Mach 1.4 and beyond. How? We talk to the head of aerodynamics
27 PRATT & MILLER Motorsport and defense makes a potent mixture
28 AOS High-speed cameras for wind tunnels
29 WIND TUNNEL SOLUTIONS Dynamotive Ltd. & ReACT Technologies Inc. join forces
30 AERODYNAMIC GOLF Who would have thought of a low-drag golf club? Adams Golf did, and the designers tell us how
34 AMERICA’S CUP SECRETS Few know that Team New Zealand’s success started here. North Sails and Auckland University team explains
38 THE MOON – AND MORE NASA’s next big challenge, by one of its engineers. Why it will test the limits of aerodynamics - affordably
44 BLADES OF GLORY Wind-driven renewable energy depends on aerodynamics. World’s only dedicated windturbine wind tunnel described
48 SMOOTH TRUCKS Dedicated heavy truck wind tunnel from Freightliner. Practical constraints drove an innovative design
52 FAN ZONE Re-fanning the historic ONERA wind tunnel. How a 56-year-old legend got a heart transplant Editor Rex Greenslade, firstname.lastname@example.org Direct: +1 248 346 6242 Wind Tunnel International — Editorial office 330 East Maple Road, Suite 170, Birmingham, MI 48009, USA Publisher Ian Stone, email@example.com Leading Edge Events & Media Ltd 100A High Street, Hampton, Middlesex, TW12 2ST. UK T +44 (0) 208 783 2399, F +44 (0) 208 979 4597 Marketing Director Jeremy Whittingham, firstname.lastname@example.org T +44 (0) 208 783 2399
2009 | WIND TUNNEL INTERNATIONAL
56 HIGH-VALUE, LOW-COST
The potential of modern CFD methods at Cranfield University: much higher accuracy at moderate computational cost
60 AVOIDING ICING STALL Pilot training to raise awareness of icing effects. An effective route to safer skies
66 PROFILE: AIR2TUNNEL Sky-diving without moving an inch
68 RIDE-HEIGHT RITE HBM examines effects of ride-height dynamics on race-car downforce
72 SOUND SCIENCE Novel experimental methods from Microflown, the world’s only acoustic particle velocity in-air sensor
76 TRICK OF THE LIGHT Cooke Corporation explains that the basic principles of high-speed cameras can be traced back 150 years or more
78 ACCURACY, EFFICIENCY New data acquisition, control and computer systems at RUAG Aerospace equals accuracy, repeatability and efficiency
82 PROFILE: WINDSHEAR Full-scale rolling-road wind tunnel serves needs of motorsport
86 THE CASE FOR PIV Real-time measurement of velocity flow fields by PIV. LaVision argues the case for its supporters
90 RAM EFFECT WITHOUT MOVING To simulate dynamic pressure effects on an F1 engine, SBI took the wind tunnel to the engine test cell
94 PROFILE: GET ME DATA – AND FAST Data acquisition for the 21st Century from Bustec
96 COMMON GROUND: TECHNOLOGY Yesterday’s technology simply will not satisfy today’s test objectives. Jacobs Technology provides a cross-industry perspective
100 AIRBUS Large low-speed wind tunnel offers solutions beyond aviation
102 CESTOL TESTING Complex Cruise Efficient, Short Take-Off and Land (CESTOL) wind-tunnel model by Cal Poly and Paterson Labs
106 TRAINS, BUILDINGS, BIKES
Examples of non-aeronautical testing missions at VZLÚ Aeronautical Research and Test Institute
110 LESS IS MORE
Advantages of using DSP hardware and software for both control and data acquisition according to Pacific Instruments
How the Supersonic Tunnel Association promotes operational excellence in wind tunnels
114 PROFILE: ELD
Engineering Laboratory Design supplies research and educational institutions and manufacturing industry worldwide
116 FIVE KEYS
Technology imperatives for large-belt, rolling road wind tunnels by MTS
119 MODEL BEHAVIOR
Tri-Models is a premier supplier of wind tunnel models and ground test hardware for the global aerospace community
122 “SMART” MODELS
NLR’s models facilitate tests that otherwise would be time-consuming or even hard to accomplish at all
The Subsonic Aerodynamic Testing Association provides the interchange of ideas, techniques, and solutions of problems
126 AERO ATHLETES
At Southampton University, some of the world’s leading athletes Improve their chances of winning through aero optimization
129 PROFILE: HORIBA
The HORIBA Wind Tunnel Balance System together with integrated moving ground system
132 MODULARITY OF DESIGN
Werum’s modular wind-tunnel control system is at the heart of Audi AG’s wind-tunnel centre in Ingolstadt
136 PROFILE: BAE SYSTEMS
BAE’s renowned aero testing facilities are now available to industries outside aerospace
A look back at the heritage of aerodynamics. This issue: a homage to soon-to-be-demolished Langley 30X60
Project Managers David John, email@example.com T +44 (0) 208 783 2399 Paul Love, firstname.lastname@example.org T +44 (0) 208 783 2399 Administration Jini Stone, email@example.com T +44 (0) 208 783 2399 DESIGN and Production Dean Cook, firstname.lastname@example.org The Magazine Production Company T +44 (0)1273 467579 Printed in England by Warners Midlands Plc © 2009, Leading Edge Events & Media Ltd. All rights reserved.
www.windtunnelinternational.com Wind Tunnel International (WTI) is a publication of Leading Edge Events & Media Ltd and has used its best efforts in collecting and preparing material for inclusion in Wind Tunnel International (WTI). Leading Edge Events & Media Ltd can not and does not warrant that the information contained in this product is complete or accurate and does not assume and hereby disclaims, liability to any person for any loss or damage caused by errors or omissions in Wind Tunnel International (WTI) whether such errors or omissions result from negligence, accident or any other cause. This publication may not be reproduced or copied in whole or in part by any means without the express permission of Leading Edge Events & Media Ltd.
Wind Tunnel Models for powered propeller simulation
Propeller (CROR) models & test rigs Carbon composite propellers Rotating balances Telemetry systems Airbridges Mass flow control units Remote control systems For info please contact: Henri Vos, tel. +31 527 24 87 22, email@example.com or firstname.lastname@example.org www.nlr.nl
News, comment and latest developments in wind tunnels and aerodynamic research and development 2009 ANNUAL REVIEW
WELCOME TO: WIND TUNNEL INTERNATIONAL
he chances are that you’re reading this as a professional involved in some way in the business of wind tunnels or aerodynamics. In creating Wind Tunnel International our aim was to bring together, for the first time, a news medium specifically tailored to your needs and interests. The chances are that you’re an engineer or an aerodynamicist but you could easily also be a facility operator, a supplier of technology or a scientific professional. Wind Tunnel International is the brainchild of Publisher Ian Stone who realized some years ago just how many industries there are for which wind tunnel testing and aerodynamic development is so important. The initial result was the wildly successful 1st Global Wind Tunnel Symposium 2008, held in Fort Worth, Texas in late 2008. Now we come to the inaugural issue of Wind Tunnel International where we’ve tried hard in the editorial content to reflect the remarkable breadth of industry applications of wind tunnel and aerodynamic technologies. I thank all the contributors and writers who made this edition so broad and interesting in content. We all know and intuitively understand aerodynamic connection relating to aviation, aerospace and automobiles but the applicability to alternative energy, building architecture, heavy duty trucks, high-speed trains, America’s Cup sails might be less obvious. And, even just a few years ago, who would have thought of cyclists honing their riding positions in the wind tunnel for lowest drag or golf club manufacturers similarly heading to aerodynamic facilities to increase club-head speed? In helping coordinate the creation of this first issue, I’ve been struck by the enthusiasm of everyone involved in this community. Unlike most things in engineering you can’t see what you’re working to affect (airflow) but you can certainly see the effects. Perhaps that’s why I hear, time and time again, descriptors like intriguing or fascinating: that aerodynamics is fun. Most of us discovered aerodynamics at any early age, I suspect. Like drag: the first time you stuck your hand out of a car window. And lift: when you made your first paper airplane in elementary school. And lift and drag together: when your hat blew off at the football game. Yes, aerodynamics is fun. But it’s also deadly serious, like when icing effects make aircraft difficult to control and contribute to fatal air crashes, or astronauts head for the moon completely comfortable that when their craft re-enters the Earth’s atmosphere at hypersonic speeds they’re not going to burn up. And when the tiniest surface improvement to a device can offset the effects of human industrial actions on global climate change. As I write this, it’s interesting to ponder how often aerodynamic issues have touched my life. As a journalist in the ‘70s, I remember investigating and explaining the (then) breakthrough of ground-effect aerodynamics in Formula 1 racing. As a race-car driver in 1981, we spent a day in the wind-tunnel (searching for downforce) and jumped three rows of the grid at the next British Touring Car Championship round. And I particularly remember the fascination, as a passenger in a Swedish Air Force Saab Viggen, of watching the pressure wave as we broke the sound barrier move along the fuselage, canopy and wings. It all came back to me when, sitting in the back seat of a BMW 3-Series convertible in BMW’s stunning new Aerodynamic Test Center earlier this summer, someone handed me a series Saab Viggen, 1980 of shapes on sticks that you could poke out into the airflow. They were running the tunnel at only about 50 km/h or 30 mi/h but the airflow could easily whip the non-aerodynamic ones out of your hand. BMW ATC, 2009 Everyone laughed. You see – aerodynamics is fun. Then we went next door and learned how BMW has slashed aerodynamic drag by 30 percent on that car over the last 20 years or so and, with other technical improvements, slashed fuel consumption (and hence greenhouse gases) by 28 percent. Now that’s deadly serious. I hope you enjoy this first edition of Wind Tunnel International. If you do, write to me at email@example.com and let me know. We want to hear from you and we’ll publish a selection of your comments into our next issue in early 2010. Rex M. Greenslade, Editor Wind Tunnel International
2009 | WIND TUNNEL INTERNATIONAL
Sikorsky X2: High-Speed Tests Next West Palm Beach, Fla. — Aiming to achieve the highest speed ever recorded for a helicopter, Sikorsky Aircraft Corp.’s X2 Technology™ demonstrator has relocated to the company’s Florida flight facility as it begins the next phases of testing in the experimental program. The X2 Technology demonstrator combines an integrated suite of technologies intended to advance the state-of-the-art, counterrotating coaxial rotor helicopter. Among the
innovative technologies the X2 Technology demonstrator employs are: counter-rotating rigid rotor blades; hub drag reduction; active vibration control; and an integrated auxiliary propulsion system. It is designed to demonstrate a helicopter can cruise comfortably at 250 knots (about twice the speed of present helicopters) while retaining such desirable attributes as excellent low speed handling, efficient hovering, and a seamless and simple transition to high speed.
Hexagonal wind tunnel to look at tornadoes London, Ontario — The world’s first hexagonal wind tunnel, home to research that aims to protect us from storms and harness the power of wind, will be built at The University of Western Ontario, in London, supported by funding from the Canada Foundation for Innovation (CFI). The project, led by Western Engineering professor Horia Hangan, received $9.5 million toward the total cost of $23.6 million. The Wind Engineering, Energy and Environment
For the past three years, the X2 Technology demonstrator program has been located at the Sikorsky Global Helicopters operation in Horseheads, N.Y., where the demonstrator achieved first flight last year. The demonstrator recently completed test flights with a fully engaged propeller for the first time. “The move to Sikorsky’s West Palm Beach facility signifies a major turning point in this program as we have officially concluded Phase One testing,” said Jim Kagdis, Program Manager, Sikorsky Advanced Programs. “Now we will fully test the integrated system to include the coaxial main rotor dynamic system with pusher propeller, and we’ll look to validate the key performance parameters of high speed, low noise, low vibration and low pilot workload. We have a lot of work ahead of us, and the Florida facility will provide ample room and a climate that will serve this program well as it moves toward the 250-knot milestone,” Kagdis said.
2010 MIRA Aero Conference Announced The 8th MIRA International Vehicle Aerodynamics conference returns in October 2010, with a focus on interrogating what the latest aerodynamic developments bring to the low-carbon debate.
(WindEEE) Dome’s unique shape will make it the first facility capable of physically simulating
The biennial event, which is firmly
spinning wind systems such as tornadoes. These and other forms of wind cannot be
established as the forum to discover
created in traditional wind tunnels.
the latest trends in all areas of
The WindEEE Dome will be used to understand pollutant and contaminant dispersal, wind
aerodynamic development, brings
effects on agricultural crops and forests, optimal positioning for wind farms and turbines,
together stakeholders throughout the
and for measuring the impact of wind on buildings, wind turbines and agricultural crops.
aerodynamics community to ensure
“The funding of these four projects demonstrates the dynamic variety of world-class
all sides of the discussion are robustly
science and research being done at Western,” said Ed Holder, Member of Parliament for
discussed. Show organizers MIRA say
London West. “The WindEEE Dome will produce many scientific knowledge breakthroughs
that the conference will have wide appeal,
and world-first discoveries. This exciting science will save lives, and it will be done right
whether prospective attendees’ focus is
here in London. Western continues its position as a global player which will attract and
on the highest fuel economy, new levels
retain brilliant minds in London.”
of refinement or the fastest lap time. WIND TUNNEL INTERNATIONAL | 2009
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Open Rotor Jets Testing – Again Evendale, Ohio — One of the most promising yet unrealized jet engine technologies has been revived this summer when GE Aviation and NASA began a wind-tunnel test program to evaluate counterrotating fan-blade systems for “open rotor” jet engine designs. This follows several months refurbishing a special NASA test rig. The testing will be conducted throughout 2009 and early 2010 at wind tunnel facilities at NASA’s Glenn Research Open rotor engine Center in Cleveland, Ohio. This is not a full engine test, but a component rig test to evaluate subscale fan systems using GE’s and NASA’s advanced computational tools and data acquisition systems. In the 1980s, GE successfully ground-tested and flew an open-rotor jet engine (the GE36) that demonstrated fuel savings GE36 engines in 1980s flight test of more than 30 percent compared with similar-sized, Open rotor airfoil test rig, recently refurbished jet engines with conventional, ducted front fan systems. The enormous efficiency from bypass air created by this fan system drove the GE36’s dramatic fuel savings. As fuel prices fell sharply in the late 1980s and early 1990s, the GE36 was never launched commercially, though it was recognized worldwide as a technology breakthrough. Since then, GE has dramatically advanced its computational aeroacoustic analysis tools to better GE and the Fundamental understand and improve open- Aeronautics Program of NASA’s Aeronautics Research Mission rotor systems. “The tests mark a new journey Directorate in Washington are for GE and NASA in the world jointly funding the program. Snecma of open rotor technology,” said (SAFRAN Group) of France, GE’s David Joyce, president of GE longtime 50/50 partner in CFM Aviation. “These tests will help International, a highly successful to tell us how confident we are in joint company, will participate with meeting the technical challenges fan blade designs. of an open-rotor architecture. It’s For the NASA tests, GE will run a journey driven by a need to two rows of counter-rotating fan sharply reduce fuel consumption blades, with 12 blades in the front row and 10 blades in the back row. in future aircraft.” 8
The composite fan blades are 1/5 subscale in size. They will be tested in simulated flight conditions in Glenn’s low-speed wind tunnel to simulate low-altitude aircraft speeds for acoustic evaluation, and also in Glenn’s high-speed wind tunnel to simulate highaltitude cruise conditions in order to evaluate blade efficiency and performance. Engine noise is a prime challenge in operating open-rotor engines in a commercial aviation environment.
NASA’s test rig, now refurbished and modernized, was actually used in the 1980s when NASA and GE first tested scale-model, counter-rotating fan systems that led to the development of the open rotor GE36 engine. The first wind-tunnel tests this summer will essentially reenact those 1980s tests. GE and NASA will first run blades of the same design that led to the original GE36 jet engine. This will establish critically important baseline data for GE for flight test correlation because the GE36 in the 1980s flew on Boeing 727 and MD-80 aircraft. As new and more exotic fan blade designs are run in the wind tunnel, GE and NASA will be able to assess comprehensive aero and acoustic design space in order to better understand how these designs will perform in an actual operating environment. In total, GE and NASA will run six different sets of blades in the NASA wind tunnels, including five sets of modern blade designs. GE designed and fabricated the scale-model blades at its Cincinnati facility using technical input provided by the GE Corporate Research Center in New York. Open-rotor jet engine designs are among the longer-term technologies being evaluated for LEAP-X, CFM International’s (GE/Snecma) technology program focusing on future advances for next-generation CFM56 engines. Boeing, Rolls-Royce, RUAG Aerospace and Deharde Maschinenbau in 2008 announced a collaborative research agreement to explore the potential of fuelefficient open-fan (open rotor) propulsion technology for future commercial airplanes. Tests of a model concept airplane with open-fan engines are planned for early in 2010 at the RUAG Low Speed Wind Tunnel in Emmen, Switzerland.
WIND TUNNEL INTERNATIONAL | 2009
BUY BIKE, GET WIND-TUNNEL (TIME)
Sarah Haskins testing in the A2 wind tunnel
If there’s one sport which has embraced aerodynamics more than any other, it’s cycling. See, for instance, our article (pages 130-133) from Southampton University describing its contribution to the UK’s stunning success in cycling at the Beijing Olympics. Now we learn that not only will buyers of a new TriadTM multisport/time trial bike from Blue Competition Cycles in Norcross, Ga. get a machine that will cut through the air with the precision of wind-tunnel-tuned geometry and tube shapes — they’ll also have a chance to learn how they can be as aerodynamic as possible with a free hour in the A2 Wind Tunnel in Charlotte, N.C. Blue started the offer last year and plan to expand it next year. After a consumer who’s purchased a Blue Triad complete build bike/ Triad SL frame set/complete bike has returned the warranty card, they receive a gift certificate to use in the A2 wind tunnel. Additional time can be purchased at a discount when testing beyond basic body positioning is desired. Internationally, Blue has an agreement with Drag2Zero and the two tunnels they partner with — Brawn GP F1 scale tunnel and the Cranfield University tunnel in Shrivenham, England. “We know that more than 80 percent of total drag comes from the rider, not the bike. That’s why we spend a lot of time in the wind tunnel perfecting our bikes and working with sponsored athletes to optimize their riding position,” said Chance Regina of Blue Competition Cycles. “When a cyclist buys a 2009 | WIND TUNNEL INTERNATIONAL
bike of this caliber, they are clearly serious about speed and efficiency. We want our Triad customers to get the most from the bike, so we’re giving them the opportunity to do the same type of wind tunnel optimization as the pros.” Wind tunnel optimization has a tremendous effect on a rider’s speed and efficiency, according to Mike Giraud, Bicycle Specialist at the A2 Wind Tunnel. “Anywhere from 70-90 percent of a rider’s power output is used to overcome wind resistance. Positioning is extremely important
for cyclist to be able to minimize drag while still producing maximum power. “For example, we recently compared a traditional road bike riding position with the same rider on a time trial bike,” Giraud said. “At 40 kilometers per hour, the rider used 24 percent less power, measured in wattage, on the time trial machine. Clearly, finding the best riding position is critical to maximizing results for both professional and serious amateur riders.”
Future Meets The Past At Langley This summer engineers have been testing a small-scale blended wing body prototype in an historic wind tunnel that once hosted some of America’s greatest aviation pioneers, including Orville Wright, Howard Hughes and Charles Lindbergh. The 21-foot wingspan X-48, a NASA, Boeing and U.S. Air Force project, was installed in the Langley FullScale Tunnel for more than a month. Engineers assessed aerodynamic effects of acoustic modifications to the vehicle. 9
STARCS is ONE
Stockholm, Sweden — STARCS (Sjöland & Thyselius Aerodynamic Research Center AB), formed from the department for experimental aerodynamics at the Aeronautical Research Institute of Sweden (FFA), recently celebrated its first anniversary. Including the same staff and resources as under the previous organization, but now privately owned, STARCS, which is located by the internationally connected Stockholm-Bromma airport just outside Stockholm, Sweden, represents a business that has been run as a research institute specialized in experimental aerodynamics for 70 years and that has gained a world reputation as a respected institution for aerodynamic research and development. The company holds five wind tunnels spanning speeds from subsonic to hypersonic and a state-of-the art turbomachine compressor test rig. It offers services in three principal business areas; Aeronautics, Space and Energy. STARCS’ expertise cover all aspects of aerodynamics within and across these areas, especially experimental aerodynamics, flight mechanics and measurement technique. STARCS continues to maintain FFA’s position as the principal supplier of services within experimental aerodynamics to many of the largest companies in the Scandinavian defence industry, including Saab and Volvo Aero. The hypersonic wind tunnel has also been used to support the development of the European space programme including
Missile release testing of the “Saab JAS39 Gripen” fighter aircraft using STARCS unique “Motorized Sting Arm”
the Arian 5 space launcher. The formation of STARCS also meant that the new business area “Energy” was defined, specifically targeting the growing need for aerodynamic development services in energy and environmentally focused markets like the wind energy and road vehicle industry in particular.
Study of unsteady flow phenomena on the Ariane 5 launch vehicle in STARCS transonic wind tunnel T1500
Controllable trailing edge flaps reduce loads on wind turbine blades Roskilde, Denmark — The considerable dynamic loads that large wind turbine blades are exposed to during operation can be reduced by manufacturing the trailing edge of their blades in an elastic material, research at the Risø National Laboratory for Sustainable Energy, Technical University of Denmark, indicates. The elastic material, made from rubber, makes it possible to control the shape of the blade’s trailing edge. “Providing the blade with a movable trailing edge it is possible to control the load on wind turbine components,” explained Helge
Profile section with a controllable, flexible trailing edge, which is controlled from measurements of inflow to the blade using a Pitot tube attached to the front edge of the blade section (left) or a trailing edge operated from the load on a small profile section mounted in front of the main blade (right)
Aagaard Madsen, Research Specialist on
trailing edge moves.
the blade and extend the life time of the
the project. “This is similar to the technique
“In this project a number of different
There has been significant development
prototypes have been manufactured with
used on aircrafts, where flaps regulate the since 2004, when Risø DTU applied for
a chord length of 15 cm and a length of 30
lift during the most critical times such as at
the first patent for this basic technique.
cm. The best version shows very promising
take-off and landing.”
Part of the research has been aimed at results in terms of deflection and in terms
With the Risø DTU innovation, however,
the design and development of a robust
there is a difference. Whereas on aircraft,
controllable trailing edge. This has now led
The size of the prototype fits a blade airfoil
movable flaps are non-deformable elements
to the manufacturing of a trailing edge of
section with a chord of one metre and such
hinged to the trailing edge of the main wing,
rubber with built-in cavities that are fibre-
a blade section is now being produced and
in this new technique the trailing edge is
reinforced. The cavities in combination with
is going to be tested inside a wind tunnel.
constructed in elastic material and is an
the directional fibre reinforcement provide
“If the results confirm our estimated
integrated part of the main blade. This
the desired movement of the trailing edge,
performance, we will test the rubber trailing
means a continuous surface of the profile when the cavities are being put under
edge on a full-scale wind turbine within a few
on the wind turbine blade even when the pressure by air or water.
years,” said Madsen.
of the speed of the deflection” said Madsen.
WIND TUNNEL INTERNATIONAL | 2009
XCOR AEROSPACE TESTS LYNX AERODYNAMIC DESIGN IN USAF WIND TUNNEL
Dayton, Ohio — A series of wind tunnel tests of the aerodynamic design of the XCOR Lynx suborbital launch vehicle was completed at the U.S. Air Force test facility located at WrightPatterson Air Base near Dayton, Ohio, using an all-metal 1/16th scale model. “Ever since the Wright Brothers pioneered wind tunnel testing here in Dayton, aerospace engineers have used it as a tool to improve aerodynamic design,” said XCOR Aerospace CEO Jeff Greason. “Computational Fluid Dynamics and other computer design tools are very useful, but you have to build real models and let real air flow around them to
get real results. We are grateful that the U.S. Air Force made this facility available to do our first subsonic wind tunnel testing under a Cooperative Research and Development Agreement (CRADA).” The Lynx, which is designed to safely fly to the edge of space and back multiple times a day, is expected to make its first flight in 2010. Greason said that the XCOR team has taken the model and data back to their Mojave, California base to analyze the results. Because the Lynx is designed to travel at supersonic as well as subsonic speeds, refined models of the vehicle will be built and tested in a supersonic wind tunnel later this year. “The CRADA allows us to form productive partnerships between the U.S. Air Force and private sector companies,” says Barry Hellman, an aerospace engineer at the Air Vehicles Directorate of the Air Force Research
Laboratory (AFRL) at Wright Patterson AFB. “We will work together to develop the aerodynamics of the Lynx which will provide valuable knowledge to help the Air Force develop future access to space systems.” Greason said that in return for the subsonic wind tunnel testing, the AFRL will get access to the data derived from the process. XCOR has already won several contracts with the AFRL, including a Phase II Small Business Innovation Research contract to supply operational data from the Lynx which will help in the development of operationally responsive space craft. “We are at a very exciting point in the Lynx program,” he said. “While we are refining the aerodynamic design, we are making progress in fabricating the Lynx’s crew cabin, testing cryogenic pumps that will be used in the propulsion system, and continuing the test program of the liquid fuel rocket engines that will propel the Lynx to the edge of space. We are making concrete progress in turning our dream of affordable space access into reality for the participants who have already bought tickets and all of our future clients.”
Maple seeds fly like … animals The twirling seeds of maple trees spin like miniature helicopters as they fall to the ground. Because the seeds descend slowly as they swirl, they can be carried aloft by the wind and dispersed over great distances. Just how the seeds manage to fall so slowly, however, has mystified scientists.
the descent of future planetary probes
In research published in the June 12 issue
and flown successfully with wing spans of
of the journal Science, researchers from
roughly a meter, but never at the scale of
Wageningen University in the Netherlands
a maple seed.
exploring the atmospheres of planets such as Mars—and of micro-helicopters. “Maple seeds could represent the most basic and simple design for a miniature helicopter, if the swirling wing could be powered by a micromotor,” says Lentink. Single-rotor helicopters have been built
and the California Institute of Technology
“There is enormous interest in the
(Caltech) describe the aerodynamic secret.
development of micro air vehicles, which,
The research revealed that, by swirling,
because of their size, must function using the same physical principles employed by
maple seeds generate a leading-edge vortex as they spin slowly to the ground. This vortex
Photos: courtesy of David Lentink
small, natural flying devices such as insects
lowers the air pressure over the upper surface of the maple seed,
and maple seeds,” says Dickinson. For example, Lockheed Martin
generating lift to offset gravity. The vortex doubles the lift generated
attempted to develop inexpensive “maple seed drone cameras” that
by the seeds compared to non-swirling seeds.
could be deployed in large numbers for surveillance, “although the
This use of a leading-edge vortex to increase lift is remarkably project is no longer funded,” Lentink says. similar to the trick employed by insects, bats, and hummingbirds
“This is still an open challenge for future aerospace engineers, and
when they sweep their wings back and forth to hover. The finding
our aerodynamic study of maple seeds could help design the first
means that plants and animals have converged evolutionarily on an successful powered ‘maple’ helicopters,” he adds. Over the past four identical aerodynamic solution for improving their flight performance. years, Lentink, an aerospace engineer, has designed operational The research might have implications for the design of swirling parachutes—which have been designed by space agencies to slow 2009 | WIND TUNNEL INTERNATIONAL
flying, flapping, and morphing micro air vehicles, inspired by his insect and bird flight research.
NEW ADVANCED WIND TURBINE DRIVETRAIN TECHNOLOGY
Cedar Park, Texas — Viryd Technologies Inc. (Viryd), a wind turbine technology company dedicated to improving drivetrain technology, announced it has received a notice of intent to award a grant from the U.S. Department of Energy to test an eight-kilowatt wind turbine equipped with its NuVinci continuously variable planetary (CVP) technology. Additionally, the company announced the re-opening of its Series A financing round. Viryd drivetrains for wind turbines leverage an advanced CVP transmission technology, developed by Fallbrook Technologies Inc., to improve energy capture by controlling the rotor to optimize its Tip Speed Ratio (TSR) at all wind velocities. The Viryd design also eliminates the need for expensive power electronics and inverters because it allows the use of an inexpensive and reliable generator that connects directly to the utility grid. Created initially as a subsidiary of Fallbrook Technologies Inc., Viryd became an independent company in 2007. Viryd’s initial products include innovative wind turbine drivetrains and complete small wind turbines based on Fallbrook’s patented and award-winning NuVinci® technology. The National Renewable Energy Laboratory (NREL) will direct the turbine testing as part of the DOE program to enhance the federal government’s ability to support the wind
industry through testing the performance and reliability of current and next-generation wind turbine drivetrain systems. Viryd’s drivetrain promises to increase energy generation, lower costs and boost small wind system reliability. “With support from DOE and our investors, we plan to perform NREL standard tests of our initial product at the National Wind Testing Center facility in Colorado in order to speed product certification and communicate the value of our small wind systems,” said Viryd CEO, John Langdon. “Our advanced technology drivetrain will allow us to capture more energy with lower initial cost — ultimately reducing the cost of renewable electricity.”
Exa Streamlines, Accelerates Simulation Model Preparation Process
Burlington, Mass. — Fluids simulation (CAE/CFD) software for product engineering innovator Exa® Corporation has released PowerDELTA™, the latest product in its suite of integrated tools that enhance the product development process. Exa says that PowerDELTA dramatically streamlines and automates the simulation model creation process by enabling the numerous, often lengthy, meshing tasks to be performed in a single, easyto-use, integrated application. Native CAD data of varying levels of complexity or completeness are rapidly and easily transformed using a sequence of parametric geometry and meshing features into high quality, simulationready meshes. With PowerDELTA, design changes are rapidly propagated through the simulation model to generate updated meshes — a huge, time saving, benefit.
HOW DO BUMBLEBEES FLY? THEY… ER… BUMBLE Unlike soaring eagles, graceful butterflies, and swiftly swooping bats, bumblebees are heavy and wide. Their wings are short. And, according to the new study, the first to look at real bees instead of insect robots or computer models, one wing flaps out of synch from the other.
Thomas and colleagues set up a wind tunnel that was 1.5 meters (about 5 feet) long, with flowers on one end and a beehive on the other. As 100 trained bees buzzed their way through the tunnel, high-speed cameras captured up to 2,000 frames each second. Lines of smoke filled the tunnel, allowing the scientists to study vortexes formed around each flapping bee wing.
According to the Discovery Channel, the work suggests that bees sacrifice
Af ter many hours of analysis, the
aerodynamics for precision as they navigate
researchers were surprised to see the left
from flower to flower, said Adrian Thomas, a
and right wings operating independently.
biomechanics professor in the department
Bees didn’t use their entire wingspans to
of zoology at the University of Oxford, U.K.
generate lift, making them less efficient than they could have been.
As early as 1919, some aerodynamicists
“Brute force may well be the answer in
argued that, according to the laws of physics, bees shouldn’t be able to fly at all.
how airplanes and some birds fly -- simply
many cases where efficiency isn’t important,”
Yet, they obviously do. One finding is that
don’t apply to bees, which flap their wings
Thomas said. “Efficiency is important for the
basic rules of aerodynamics -- which explain
200 times a second.
hive, not for an individual bee.”
WIND TUNNEL INTERNATIONAL | 2009
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Inside BMW’s main tunnel, looking upstream from the air return with the airfoil collector system in foreground. Note the grilles in the far wall, concealing Helmholtz resonators to eliminate low-frequency noise
The Answer is
Blowing in the Wind Every automotive manufacturer is facing challenges: societal concerns on greenhouse gases; seemingly ever-increasing gas and raw material prices; and more and more restrictive legislation on safety. Some see the cars of tomorrow being bland, boring and characterless. But not BMW. It recently finished constructing the world’s most advanced automotive aerodynamic development facility and says the solutions found there will be vital to staying true to the brand’s vision of “Sheer Driving Pleasure”. BMW explained how to Wind Tunnel International’s Editor Rex Greenslade at the center’s dedication
estled away in a suburb of Munich, Germany, on the edge of BMW Group’s technical campus it sits like a curious architectural tour de force. Consisting of two toroidal rings, one with its major axis horizontal, the other vertical, like links of a huge chain, its purpose is not immediately apparent and the signs, in typical German fashion, discreetly unobtrusive. But the distinctive design clearly indicates that something very special is taking place inside.
It’s the new, state-of-the-art BMW Aerodynamic Test Center (ATC) and each of the rings is, in fact, a recirculating wind tunnel. The one oriented horizontally is a full-scale wind tunnel, with no fewer than five rolling roads to aid boundary layer simulation, and the vertical 14
one (the BMW “AEROLAB”) a scale-model tunnel featuring a huge 9 x 3.20m (29.5 x 10.5 ft) moving belt, large enough even to test two car models at the same time. The stunning architectural configuration is the result of typical BMW Group thinking. Real estate was limited in availability, BMW and MINI needed two tunnels, ergo link them together in this innovative way, reaping maximum operational efficiency for a given investment. Oh, and by the way, make an architectural statement at the same time. Anyone following BMW Group’s history should not be surprised by the clarity of thinking and single-minded execution that the design of the ATC represents. Of all automotive manufacturers, BMW has pursued its corporate vision more clearly and more consistently than any other: to produce the Ultimate Driving Machine (sometimes WIND TUNNEL INTERNATIONAL | 2009
The BMW ATC’s stunning external architecture. Something special happens inside ...
expressed as “Sheer Driving Pleasure”). This strategy, developed in the early ‘80s, is much more than a slogan, it defines a corporate way of life that’s been zealously protected and pursued for more than a generation. Experts consistently rate BMW and MINI highest of all car makers for the degree of driver “engagement” that its products provide. In terms of profitability and market growth, the results have been spectacularly successful. Yet is such a vision sustainable in a changing world, where regulatory realities of exhaust emissions and CO2 limits and market pressures from fuel costs seem to run counter? BMW’s performance suggests that it can. Both today and in a long-term comparison, the BMW Group claims that BMW and MINI are far ahead of all competitors in the premium segment in reducing both fuel consumption and CO2 emissions. On a European level this is borne out, among other things, by a reduction of fleet consumption between 1995 and 2008 of far more than 25 per cent, meaning that the BMW Group with the BMW and MINI brands has already over-fulfilled the commitment made by the Association of European Automobile Manufacturers (ACEA). BMW says that ongoing reduction of fuel consumption and emissions calls time 2009 | WIND TUNNEL INTERNATIONAL
and again for new, massive investments in the Company’s research and development facilities, resulting in an above-average commitment in offering Sheer Driving Pleasure on even less fuel and with even lower emissions. Like it original vision, which remains, its evolved product strategy called “EfficientDynamics” does not call for short-term actions or new priorities and is exceptionally well articulated. It’s a fundamental, all-round philosophy including all innovations with the result of consistently reducing fuel consumption and emissions for a new car model versus the former version and, at the same time, enhance road performance to an even higher standard. Optimisation of vehicle efficiency is a guideline applied by the BMW Group in all areas of vehicle development, including: powertrain, transmission and suspension technology; the intelligent flow of energy within the vehicle as well as the intelligent choice of materials for superior lightweight construction; and ensuring the permanent optimisation of aerodynamics. The ATC represents an investment of €170 million (approx. $243 million), was constructed over a three-year period and is now home to 500 BMW staff. It clearly confirms BMW’s consistent
quest for further progress in the context of EfficientDynamics and to protect what it sees as its position as the world’s most successful manufacturer of premium cars. Optimisation of the car’s aerodynamic qualities is a fundamental factor today in the development of new models for it improves both performance and efficiency, as well as the driving stability offered by the car on the road. A reduction of air drag by 10 per cent, for instance, offers the customer a reduction in fuel consumption on the road by more than 2.5 per cent; that may not sound very much to the car buyer but aerodynamicists and engineers know that’s very significant, particularly if such gains can be reaped year over year. Aerodynamic research at BMW since the early ‘80s has been carried out at its Aschheim wind tunnel on the outskirts of Munich, as well as other BMW and non-BMW facilities (see side-bar interview with Head of Aerodynamics Hans Kerschbaum). The ATC, however, is located in the immediate vicinity of the BMW Group’s Research and Innovation Centre (FIZ) meaning that the BMW Group’s aero¬dynamic specialists now will be working next door and hand-in-hand with BMW’s designers, constructors, engine specialists and other experts. 15
The main tunnel showing the five rolling roads — one for each wheel and a moving belt for the underbody
Technicians working on the wheel mounting system. Wheels in the AEROLAB are independently mounted from the car body
Over and above such enhanced integration into the development process, the ATC has facilities and capabilities unique – certainly in the automotive world – in determining aerodynamic features and qualities in a truly realistic process. One option, for example, is to analyse new models at a very early stage of development in a wide range of different situations with all test scenarios following reallife driving conditions. This means not only at different speed ranges, but also different driving situations such as driving in a bend, taking the actual movement of the body into account. A further point is that the ATC can, for the first time, render and analyse the interaction of a car with other vehicles, for example when overtaking or following closely at speed, thus offering yet another new benefit in the development of production cars. Hitherto, such tests could only be conducted on a test track, and then with cars almost at the end of their development process. Now the knowledge gained in this process can be 16
fed back into the development process much earlier, serving to optimise a new model effectively almost from the start. While drag reduction is very high on the list of performance criteria for aerodynamicists to study in an automotive wind tunnel, a wide range of other criteria is also important. Optimisation of lift forces in the interest of maximum driving stability, a precise supply of cooling air to the engine, the transmission and the brakes, the reduction of wind noise and the minimisation of dirt on the car caused by air turbulence, are among the objectives pursued by the engineer these days. For convertibles and roadsters, the minimisation of air draught within the interior when driving with the roof down is an additional important objective, while for motorcycles the reduction of buffeting and airflow instability from other vehicles is also a priority, particularly for Touring models. There is little disputing the BMW Group’s claim that its ATC is the world’s most modern
The guiding vanes for the first 90deg turn of the main tunnel’s return can be seen in the background
and advanced facility of its kind. The main ATC wind tunnel, for instance, has a 300rpm, 8-m (26.2-ft) diameter fan with a 4.4MW output to facilitate the analysis of fullsize vehicles up to 300 km/h (186 mph). The variable nozzle opening is up to 25 m2 (269 ft2) and the measuring area has dimensions (length/width/height) of 22 x 16 x 13 m (72 x 52 x 43 ft). The AEROLAB scale tunnel has a 400-rpm, 6.30-m (20.7-ft) diameter fan with a 3.8-MW output for a similar maximum wind velocity of 300 km/h (186 mph), a nozzle of up to 14 m2 (151 ft2) and a measuring area of 20 x 14 x 11 m (66 x 46 x 36 ft). In both measurement areas, the test platform can be rotated up to 30 deg. (though typical measurements are at much less yaw) to reproduce crosswind/yaw conditions. What sets the ATC apart are the innovative measures applied to faithfully reproduce, in a controlled test facility, what happens aerodynamically when the car is driven on a road. WIND TUNNEL INTERNATIONAL | 2009
In a convertible, comfort for the passengers with the roof down is a major consideration.
Improvements to the aerodynamics of a 2007 3-Series Convertible versus one of 1987 clearly show the significant improvements reaped in terms of effectively preventing air swirl and turbulence within the passenger area and maintaining effective and comfortable heating and ventilation. Note in this screenshot of a CFD animation provided by BMW how the air flow in the 2007 car is significantly less turbulent and stays much more effectively within the car envelope than in the 1987 car. This not only improves the comfort of occupants by reducing buffeting but also increases the efficiency of the heating/ventilation/air conditioning.
Does Aerodynamics really matter? In justifying its claim that it makes use of the most advanced measuring technology and innovative test procedures to make consistent progress in aerodynamic performance, BMW presented an intriguing analysis of its current 3 Series Convertible and its predecessors – together with a tantalizing look at the future (see next page) -– enabled by expected results from the ATC.
BMW 320i BMW 320i Convertible (1987) Convertible (2009) No of doors/seats Length/width/height (unladen) mm
Wheelbase mm Track, front/rear mm
Working with renowned wind-tunnel suppliers and technology leaders Jacobs Technology Inc. and MTS Systems Corporation, the BMW Group focused on two important areas – pressure distribution within the test section and the classic windtunnel boundary-layer issue existing for ground-based vehicles. Measurements showed that in conventional wind tunnels the static air pressure varies longitudinally (or axially) through the length of the test section, the variations corresponding to the expansion of the air as it leaves the nozzle, further expands into the test section and is gathered again at the collector at the air return (see accompanying graphs). These varying air pressures cause inaccuracies in the measurement of drag coefficient – in particular, the high pressure immediately before the collector could cause the drag coefficient to be underestimated because of a buoyancy effect. With Jacobs, BMW Group developed a electrically adjustable, variable 2009 | WIND TUNNEL INTERNATIONAL
Weight, unladen, to DIN kg
Drag coefficient Cd Roof closed
Cross-section A sqm Engine Configuration/cylinders Capacity cc
Max output (at engine speed) kW/hp (rpm)
Max torque (at engine speed) Nm/lb-ft (rpm)
Acceleration 0–100 km/h sec
Top speed km/h
Fuel consumption, combined, to EU ltr/100 km (Approx.)
In 1987 a BMW 3-Series convertible, with the roof closed, had a drag coefficient (Cd) of 0.39. It didn’t look a slouch aerodynamically. by any means. Yet today the same vehicle has a Cd of 0.27. Design considerations have led to increases in every vehicle dimension (resulting, among other things, in significantly greater frontal area), increased content and safety legislation has led to more weight, and power output has risen by 30 percent (with consequent improvements in performance). Despite all these increases, today’s 3 Series Convertible has 38 percent better fuel consumption than its 22-year-old predecessor. Of course, improvements in power train (engine, transmission, management) are also significant contributors but it’s easy to see why BMW places such a high priority on aerodynamics and on the potential of the ATC. 17
aerofoil collector system for the air return that manages the airflow at the collector point of the air return circuit. BMW says that its validation process of the facility – involving calibration models with the other facilities it knows so well – show that this aerofoil system works so well and can be adjusted so finely that the longitudinal air distribution is virtually constant. It’s a characteristic of the ATC that clearly makes the company’s aerodynamicists extremely proud. A side-benefit of this system is that when teamed with other noise attenuators such as Helmholtz resonators, both wind tunnels are exceptionally quiet, avoiding in particular low-frequency vibrations, and making these facilities ideal for aeroacoustic development. Both ATC wind tunnels incorporate air suction and air bleeds ahead of the test section to help manage the ground boundary layer. For ground simulation, BMW Group, collaborating with MTS, developed different approaches for the two facilities. In the full-scale tunnel, ground simulation is provided by no less than five rolling tracks. The wheels of the vehicle being studied run on small rolling sections serving to simulate the actual rotation of the car’s wheels. These rolling tracks may be varied in width and length, and therefore adjusted to vehicles of various sizes. A 10-m (32.8-ft) long track that’s variable in width from 1.0-1.1 m (3.3-3.6 ft) between the turning wheels serves additionally to render the flow of air beneath the car.. Using these five rolling tracks, the test engineer is able to determine the so-called flow-split, that is the share of air flow above and beneath as well as at the side of the vehicle, far more precisely than in a conventional wind tunnel. In the AEROLAB, BMW and MTS chose a huge rolling road: at 9 m (29.5 ft) length and 3.20 m (10.5 ft) in width it’s the same size as that of the rolling road at the Windshear facility in Concord, North Carolina. The model or models being tested can be moved from one position to the other using a balance which weighs no less than 70 tons. In fact, everything concerned with the measurement process in the AEROLAB is massive: the turntable housing the rolling road, for instance, weighs a further 40 tons, with the mass of other structures rapidly the total to 150 tons or more. The AEROLAB’s rolling road belt is made of 1-mm (0.03937-in) thick steel, laser welded into a continuous strip that rotates around two 1-m (3.1-ft) rollers. At 300 km/h (187 mi/h) maximum operating speed, the strain on the belt is significant requiring “special” steel. Air is injected beneath the belt at an overall 18
The main tunnel’s 4.4MW fan
pressure of 7 bar to create an air film between the belt and the floor below, with additional higher-pressure (24 bar) air injectors below the belt area immediately underneath the vehicle wheels. (See MTS article for more detail on this process)
BMW’s AEROLAB Air Curtain The development of every new vehicle is always a vision pointing into the future. But the primary question to be asked each time Without Air Curtain With Air Curtain is always the same: what impression will the new model have on the customer? Design and comfort, driving dynamics and efficiency – it is only on the road that the quality of the work done by the development engineers over months and years will really become evident once and for all. Aerodynamicists working in the automotive industry have to work hand-in-hand with the vehicle designer/stylist to ensure that whatever they develop is saleable in the retail marketplace. Put another way, scientific expertise interacts hand-in-hand with practical development while art and design determines shapes and architecture that will meet the product’s showroom appeal. A good example given by BMW of this work is the innovation they call the EfficientDynamics Air Curtain, a significant drag-reducing innovation that customers won’t see. In practice about 40 per cent of the overall air resistance results from the proportions and shape of the vehicle, a quarter of this factor coming, respectively, from the surface structure of the vehicle and from other features such as the mirrors, the lights, the number plate and the antennae fitted. Another 20 percent is created by air moving along the underfloor, 10 percent from air moving through the car (engine cooling, heating, ventilation and air conditioning etc.). It’s not widely understood that the balance of 30 percent comes from air turbulence caused by the rotating wheels and their associated wheel arches. The wheel arches are almost as important as the car’s overall shape…. So, at BMW, drag reduction increasingly focuses on the wheels and their associated body openings. The accuracy of the ATC enables the BMW Group’s aerodynamicists, for the first time, to clearly determine and consistently realize the great potential for optimising flow conditions in these areas. They believe that they can reduce the level of air resistance further in ways not identifiable before. The Air Curtain innovation comprises openings – approximately 10 x 3 cm (4 x 1.2 in) high and wide – at each outer end of the front air dam. Air is guided from these opening into two ducts which channel the airflow along the inside of the front air dam leading to the wheel arches. From there, the air leaves the ducts at high speed through a very small opening and is directed around and just outside the outer wheel flanks. This jetstream leaving the vehicle in this way “rests” on the WIND TUNNEL INTERNATIONAL | 2009
The main tunnel looking downstream from the nozzle. Note the boundary layer “knife” in the foreground
The size of the AEROLAB belt enables the analysis of vehicle flow conditions under all kinds of circumstances, so that aerodynamics and driving dynamics may interact and be combined with one another. The number of scenarios available as well as the claimed precision of the test processes applied at the ATC combine to produce a standard unique for the automotive industry. There is no doubt that the BMW ATC sets a new standard for the automotive industry. Exceptional accuracy, mixed with unparalleled flexibility and remarkable realism, makes for an intoxicating scientific cocktail. Will it make BMW and MINI cars better? That will, of course, depend on how it is used and the lessons learned from it are applied. But judging from BMW’s track record and unrelenting pursuit of product excellence, it’s hard to come to any conclusion other than it will. Tremendously.
Facts and Figures front wheels like a cloak or curtain – hence the name Air Curtain. This effect reduces air resistance by improving the coverage of the front wheels and, BMW says, can be measured in the AEROLAB as a significant factor. This aerodynamic curtain around the front wheels is formed without using any additional components on the wheel arches. All the observer will see from outside is the additional openings on the front air dam. A BMW 3-Series sedan has a Cd of about 0.29 when measured without rolling wheels. This falls to about 0.28 with rotating wheels and 0.27 with the proposed Air Curtain (see separate story). BMW expect that the Air Curtain will be introduced on a future model soon. And long-term, what then? A 3-Series sedan body shape without any wheels or wheel arches (what BMW calls a “flying fish” shape) has a Cd of about 0.18 – a further 35 percent reduction and a measure of the potential for wheels and wheel arch aerodynamic improvement. Rest assured that BMW will be trying its damnedest to claw back as much of that 35 percent as possible.
Start of construction ..................................................................................... December 2005 Completion of the building structure ...................................................................February 2007 Wind on in the AEROLAB ...................................................................................October 2007 Wind on in the main wind tunnel ..................................................................... December 2007 Overall amount of concrete ...................................................................................36,000 m3 Overall amount of steel ..........................................................................................6,200 tons Overall facade area ......................................................................... 18,000 m2/193,700 ft2 Total investment Building, technical equipment and facilities..........................................................Euro 170 million
Ground area .................................................................................. 25,000 m2/269,000 ft2 Length of building .............................................................................................120 m/394 ft Width of building ................................................................................................90 m/295 ft Height of building .................................................................................................22 m/72 ft No of floors........................................................................................................................ 5 Gross area .................................................................................... 32,500 m2/349,700 ft2 Gross built-up volume ...........................................................................................20,000 m3 No of workplaces ............................................................................................................500
Main Wind Tunnel
Ground area (length/width).................................................................84 x 40 m/276 x 131 ft Direction of flow . ....................................................................................................Horizontal Fan diameter.......................................................................................................8 m/26.2 ft Fan speed ...............................................................................................................300 rpm Fan output ...............................................................................................................4.4 MW Max wind velocity .................................................................................. 300 km/h (186 mph) Overall airstream volume ......................................................................................18,000 m3 Size of nozzle . ................................................18 - 25 m2 /194–269 ft2, electrically adjustable Size of measuring area (length/width/height) ...........................22 x 16 x 13 m/72 x 52 x 43 ft No of tracks .......................................................................................................................5 Size of underfloor track (length/width) ...................... 10 x 1-1.10 m (32.8 x 3.3–3.6 ft) (variable)
Ground area (length/width) . ................................................................74 x 16 m/243 x 52 ft Direction of flow . ....................................................................................................... Vertical Fan diameter . ...............................................................................................6.30 m/20.7 ft Fan speed ...............................................................................................................400 rpm Fan output ...............................................................................................................3.8 MW Max wind velocity .................................................................................. 300 km/h (186 mph) Overall airstream volume ........................................................................................6,000 m3 Size of nozzle . ...............................................................................................14 m2/151 ft2 Size of measuring area (length/width/height) ...........................20 x 14 x 11 m/66 x 46 x 36 ft No of tracks ....................................................................................................................... 1 Size of underfloor track (length/width) ............................................. 9 x 3.20 m (29.5 x 10.5 ft)
2009 | WIND TUNNEL INTERNATIONAL
Hans Kerschbaum Head of Aerodynamics BMW Group
What were your main goals when establishing BMW’s new Aerodynamic Test Centre? During the time I’ve been with BMW and responsible for aerodynamics, we have always made modifications to our original aerodynamic wind tunnel in Aschheim. For example, we had previously made upgrades to the balance, and to the aerodynamic performance,. We even modified the concrete test section plenum to increase the height. So, with the new Aerodynamic Test Center (ATC), first we wanted a very large facility, with plenty of opportunity for future modifications. With the new ATC, we have planned and built large test section plenums. They are very large and we can make changes if we need to, we have flexibility for the future. For example, we could incorporate some new measurement technology in 20 years, that does not currently exist. The second goal was to have two separate wind tunnels. The ATC features a full-scale wind tunnel with acoustic treatment in the circuit. With some minor additions, we could make this into one of the quietest aero-acoustic wind tunnels in the world, if we wish. The ATC also features a Model Wind Tunnel (the AEROLAB), that is not only for 50-percent scale models but also for full-scale vehicles. The AEROLAB could be used for fundamental aerodynamic research very early in the model development process that you never normally have the possibility to do. With the AEROLAB, we are now able to simulate what happens on the road in reality, in a repeatable and controllable wind tunnel test environment. What is the focus of that research, the areas that you really want to dig deep into? We have to reduce the vehicle aerodynamic drag. We need to find more possibilities to reduce the drag while not making too many restrictions on the styling department. For us, it wouldn’t be difficult to develop a car with a drag coefficient below 0.20. That’s not a problem, but this car would not sell very well, since it would not represent the current BMW styling. But in the future we must find a way to develop a car with such a low drag coefficient, that does reflect the BMW styling. As an example, today you see BMWs with very short overhangs ahead of the front wheels, that is a very typical BMW design feature. We don’t design vehicles that have a long nose like Porsches or the Jaguar E-Type. For aerodynamic efficiency, this is a very, very difficult design constraint. For these design themes, we must find solutions to achieve a low aerodynamic drag. When will we see the first benefits of the aerodynamic work from the ATC reach production vehicles? In one or two years, approximately. It takes a little time to understand
The sheer scale of the AEROLAB can be gauged from this view. Note that the huge rolling road is 9 m (29.5 ft) in length and 3.20 m(10.5 ft) in width. The airfoil collector system ahead of the wind tunnel return can be clearly seen at right
the wind tunnel facility and to use the facility and the integrated test systems correctly. We have integrated the latest rolling road, or moving floor belt, technology in the ATC wind tunnels to be able to better simulate the aerodynamics under the vehicle. However, this is not the first time for BMW to be working with moving belt technology. Because we had no moving belt at the original BMW aerodynamic wind tunnel (at Aschheim), we tested a lot at other wind tunnels. For example, we tested at the Swift wind tunnel near San Diego, Cal., in Pininfarina in Turin, Italy, at St. Cyr in France, at the FKFS (the university wind tunnel in Stuttgart), and at RUAG Aerospace in Emmen, Switzerland. Through the many years of working in these wind tunnels, we gained knowledge that we used to make sure we made no mistakes when planning our ATC wind tunnels. Through this work you must have gained a lot of knowledge about the correlation between wind tunnels. What can you say about your correlation work on the ATC tunnels? At the moment we are performing our validation program of the wind tunnels. We are determining what we measure in the new wind tunnels with our different cars that have already been tested in other wind tunnels. That’s the work we are doing now and we can’t say anything about the results at the moment. But in one year, we will be able to publicize results from the correlation tests. I was at a recent SATA (Subsonic Aerodynamic Test Association) conference in the United States and everyone was asking me the same question. I gave the same answer – that I’ll have the information about a year from now. What are the most important areas of a car for the aerodynamicist? The areas that produce the aerodynamic drag are most critical. About 40 percent of the drag comes from the shape and upper surface of the vehicle body, 30 percent from the wheels and wheelhouses, 20 percent from the underfloor and 10 percent from the cooling and flow through the engine compartment. Many people look at the shape and surface of the vehicle and think that the shape is responsible for the aerodynamic drag. But, the shape and upper surface are only responsible for 40 percent of the total drag. 60 percent comes from other areas. For lift force, the shape and upper surface of the vehicle has a larger effect. Wind tunnels were originally developed for the aviation and aerospace fields. What lessons can you take from these industries and apply to automotive aerodynamics? To be honest, not very much. WIND TUNNEL INTERNATIONAL | 2009
What about motorsport. Does that produce lessons or knowledge applicable to production cars? If you look at Formula 1 (F1) cars and production cars, the aerodynamics are completely different. In F1, the interest is primarily to create downforce. We are interested primarily in reducing the aerodynamic drag. F1 teams are less interested in efficiency and drag force. The BMW Sauber F1 team in Hinwil, Switzerland is completely separate from BMW AG, where we design and manufacture high quality production vehicles. However, we have racing cars like the M3 (racing in the American Le Mans Series) and we’re responsible for the aerodynamics of these cars. This is something really very interesting because our engineers first create the series production cars – like the 3-Series BMW – and then they develop the M version, and then they make the racing version. It’s exciting and rewarding work for our guys to work on these models.
When you test a motorcycle at the ATC, how do you simulate the effect of a rider? Because the rider must fundamentally effect the aerodynamics. Absolutely. The head of the motorcycle department himself has been perfectly digitized to be the rider (laughs). This is something really interesting for motorcycles. CFD is really not made for motorcycles, but we perform 80 to 90 percent of motorbike aerodynamic development work using CFD. Motorcycle aerodynamics is very functional. We do everything first in CFD and then take it to the other departments and say that it’s necessary to incorporate certain changes. Most of the time these changes get incorporated into the final design. Initially, it was, frankly, a big surprise. At first, we didn’t think CFD was the right tool for motorcycles but we have done it and been very successful.
How many people from aerodynamics would be involved in each new car program? We have one engineer who is responsible for the vehicle shape and surface, Are there any advances in flow visualization? We don’t use PIV (Particle Image Velocimetry) because there’s no need, to one who is responsible for the airflow through the engine compartment, be honest. We do use smoke for simple flow visualization demonstrations. and one trying to integrate all the information on the development project. However, to explain what happens to our management, we use CFD So usually, it requires three aerodynamicists. However, from time to time, (Computational Fluid Dynamics). We have invested significant effort in the it’s only one and then he’s responsible for everything. validation of CFD. Independent validation of CFD codes is very important since the code development companies will show you nice pictures and say Wind tunnel time is known to be very expensive. What are you doing that that this is the correct aerodynamic solution. But CFD is never 100% to make sure that you use the facility as efficiently as possible? accurate, so one must perform a lot of validation on CFD, to understand It depends a little on the engineer that’s working in the wind tunnel. In the aerodynamics department we have about 35 people. These staff members when it works, and when it may not work. We have a strategic partnership with Exa in Boston. Exa has developed must be trained very well. When they join our company, they are not a CFD code, named PowerFLOW which we have used for more than 15 responsible for their own project. Rather, they start off as team members years. With PowerFLOW, we have performed very accurate validation that learn from more experienced engineers. Wind tunnel time is very work and have gained a lot of confidence in this tool. We make scale expensive and it’s important that these are really good engineers, people models and test them in the wind tunnels and compare results with the who know what they’re doing in the wind tunnel. A test of a particular CFD calculations, with a high degree of accuracy. With this validation vehicle configuration in a wind tunnel takes only three or four minutes work, then we know that the CFD code we use is correct. We know that and then you have to do the next modification. And if there is an engineer the results and pictures we show from this CFD code, including the flow who doesn’t know what to do next, you can waste a lot of time. You must have a plan what you want to do, you must have prepared parts, and you visualization streamlines are correct. Nowadays, we speak with our management only with flow visualization must always be ready for the next step. pictures from CFD. How do you manage the interface between aerodynamics and design/styling? Is managing the data and calculations from CFD a limitation for you? First, we must know what is good and what is bad. So the aerodynamicists For instance, how long does it take to run a full CFD simulation of a complete car? make all modifications working with our designers. All our engineers working For a full car, with every detail, including flow through the engine in the wind tunnel have significant test and vehicle development experience compartment, that would take a lot of time. The question is: Is that so they know what could and what could not be proposed to the Design helpful? We don’t generally do that. We use CFD very early in the department. So most of the time the aerodynamicists explain the possibilities vehicle development process. We use the underfloor from the preceding and the opportunities for changes and improvements. Based on this, we generation car and create the computational surface based on that. We can discuss the potential changes with the Design department. Also the initially create this surface only roughly, with no details, because in designers know us, since we have been working together closely for years. the very early stages of development, the details are not important. The success of this design development process depends on the What is important are the proportions: should the roof be a little bit interactions between the designers and us. The team is important higher or lower, for example? That’s what we use CFD for – to create the and bringing the team together regularly is important. Some of our architecture of the car. In CFD, if you have the proper CAD (Computer aerodynamicists work in the Design department, for instance. If we have Aided Design) tools for generating the computational surface, then it can something of interest we go to them. We try to invite the Design department be a relatively quick process. But it still takes about one day – which members to the wind tunnel as often as possible because a good friendship is really good. is very helpful, perhaps more than any others. The problem is not to know how to make a good car – we know that – it is Much slower than testing a clay model in the wind tunnel itself? to develop that car into a good design. This is the essential difficulty. I think Yes. If we have this clay model, in one day, we can test 30 or 40 modifications. it’s the same challenge all over the world, in every automotive company. This is much quicker than the CFD. But at the end of that day, the clay CONTACT model won’t be very symmetrical and you have to take it out of the wind Hans Kerschbaum, BMW Group E-mail: email@example.com tunnel, measure it and mill it to the correct geometry. 2009 | WIND TUNNEL INTERNATIONAL
1000mph – On Land Bloodhound SSC is called an “Engineering Adventure”. What could be more appropriate for project that not only calls for breaking the sound barrier – like the World Land Speed Record Holder Thrust SSC – but to top 1000 mph. Can it be done? WTI Editor Rex Greenslade talks to Bloodhound’s Chief Aerodynamicist Ben Evans … 22
WIND TUNNEL INTERNATIONAL | 2009
hat are the main challenges aerodynamically
in creating a successful 1000 mph car?
The first one is drag. Obviously to accelerate the car to these sort of speeds you to have to look at the air resistance acting upon it. When you go supersonic, the drag on the car increases significantly. So one of the questions we had to ask was: what kind of drag would a car like this experience at Mach 1.3-1.4, which is about 1000 mph, depending on the temperature. We realized quite early on that you could design a car to do the job, do 1000 mph. The second question was: how on earth do you keep it on the ground? One’s natural instinct is that something travelling at this sort of speed should be flying, not travelling on the ground. When you’re travelling at these sort of speeds, it’s true that you can be generating massive vertical forces but you can direct those vertical forces in whatever direction you want but how finely can you control those vertical forces? You could generate an awful lot of downforce (at those speeds) and you could easily turn it into the world’s fastest plough if you got it wrong. Also, in the other direction, if the lift changed at some point in the run you could change it into an aircraft. We refer to Bloodhound as being “Mach number insensitive”. It’s impossible to design a car that has the same aerodynamic characteristics at all Mach numbers but we’ve tried to design a car that has the minimum variation in vertical forces throughout its Mach number regime. How have you addressed these challenges in your work plan? If you look at the car you’ll see it’s quite long and slender. The sharper the nose, the more slender the car, the lower the drag. It’s long (just over 14 metres long), we’ve tried to minimize the cross-sectional area of the car. And things like the wheels which are outside the car have elaborate wheel fairing on them to minimize the shock waves they’re going to cause. The really sticky one is the management of the vertical forces and, in particular, those wide-spaced rear wheels to give roll stability and the shock waves they generate. There’s a bow shock off those wheels that fans out and intersects with the back end of the car; in effect, the back end is sitting on an air cushion that’s trying to lift it up. 2009 | WIND TUNNEL INTERNATIONAL
“There’s a bow shock off those wheels that fans out and intersects with the back end of the car; in effect, the back end is sitting on an air cushion that’s trying to lift it up.”
We’ve just finished an awful lot of work — including the orientation of the suspension struts, the fairing around the wheels — on getting those bow shocks are as weak as possible: unfortunately, you can never completely get rid of them. Another sensitive area where we’ve spent a huge amount of effort is on the canopy over Andy Green, the driver. It might look like a fairly standard cockpit shape but that angle is at exactly the angle we want so that it doesn’t adversely affect other parts of the vehicle, like the inlet to the jet engine. What unique or innovative solutions have been implemented in the vehicle to address aerodynamic concerns? One of the main keys to our success will be that we’re using a combination of thrust generation. We have the combination of a device — a rocket — that gives you a massive amount of thrust for a small size and weight but is basically on or off, with a jet engine, which gives 23
“The challenge about the transonic regime is that the position of the shock waves is moving ... Predicting exactly where on the car the shock waves will be at any given mach number is much more difficult thing to do between Mach 0.7 and Mach 1 than it is when you’re completely supersonic.” you controllability, a combination which no other team has attempted before. They’ve all been either pure rocket or pure jet. Our combination of the two is going to give us a massive advantage. Another area is in terms of computational fluid dynamics (CFD) using a package completely developed here by the School of Engineering at Swansea University. It’s called FLITE, and was first developed back in the ‘60s at Swansea; we’ve adapted it for things like rotating wheels and a rolling floor. Thrust SSC was designed to travel up to 850 mph but didn’t achieve that as it experienced unexpectedly high drag which we believe came from the entraining of large amounts of dust into the airflow. You’re actually accelerating dust and other particles and thereby because of your continuity equation and your momentum equation you’re adding drag to the vehicle. So one of the innovative things we’re doing here is modelling this phenomenon which we’ve called spray drag. We’re trying to predict where dust particles will get entrained into the flow, and where those particles will travel at speed, how they will interact with the flow, what surfaces of the car they will impinge upon downstream.
Does spray drag differ significantly between different attempt locations? Yes and one of the things we’ve been very careful to do is not to design it for a given surface. You could design a wheel profile that works incredibly well on a surface like Black Rock (alkaline playa), for instance, and then find it’s useless on a much more solid surface like the Bonneville Salt Flats. There’s a big difference in the size of the particles that get entrained. One of the beauties of running with your own software package is that once you’ve decided which surface you’re going to run on you can go in and make sure the model is as close to that desert surface as possible. If you’re running a commercial package … well, to my knowledge there aren’t any commercial packages modelling particle entrainment. The effects of transitioning the sound barrier with flying objects are well understood. In comparison, the effects of passing through the sound barrier with a wheeled vehicle are not. Can you describe what these effects are? When things are subsonic, things are fairly straightforward. The air is flowing over the car, there are obviously areas of higher and lower pressure but you don’t have to worry yet about where shock waves are forming.
This series of screen shots from the CFD analysis illustrates the aerodynamic complexity as Bloodhound accelerates from Mach 0.8 to 1.49. The intensity of the shock wave (red) as the transonic regime is traversed is clearly visible
WIND TUNNEL INTERNATIONAL | 2009
Things start getting tricky when you enter the transonic regime from about Mach 0.7. At this point, some of the flow over the car has transitioned to supersonic, whereas the bulk flow is still subsonic. Air has to get around various obstacles on the car, get around the nose, around the winglets and so on, and to do so it has to accelerate through the speed of sound. To get back down to the free stream speed it has to transition through a shock wave. The challenge about the transonic regime is that the position of the shock waves is moving, because the point at which the air slows down is moving. Predicting exactly where on the car the shock waves will be at any given mach number is much more difficult thing to do between Mach 0.7 and Mach 1 than it is when you’re completely supersonic. At that point, the aerodynamics settle down and the car becomes more stable. Drag is increasing enormously but in terms of these transient phenomena things get a little easier. There are few key areas then where you’re going to see shock waves. One is the nose, the classic bow shock, a two-shock system that develops over the cockpit canopy — there’s an angled shock that comes from the front of the cockpit and then a normal 90 degree shock straight up, right in front of the intake duct — and then the shock waves at the back of the car. Basically shock waves occur wherever you have a sudden obstruction to the airflow. Which is why in design meetings, Ron and I will be arguing for keeping everything as smooth and slippery as possible, while the vehicle dynamicists will want wide wheels for roll stability purposes. How much of what happens can be inferred or anticipated from supersonic flight and how much is quite different? The big difference between what we’re trying to do and the typical supersonic aircraft, which nowadays is fairly well understood, is this problem with the ground. The way in which the shock wave interacts with the ground will depend enormously on what that ground is like. We’ve made some fairly large assumptions about what we term boundary conditions, including the porosity of the surface and things 2009 | WIND TUNNEL INTERNATIONAL
The expected time trace of a successful speed record run. Note how little of the run is actually through the measured mile (center “column”) — the rest is spent either accelerating or decelerating
What lessons did the successful Thrust SSC project teach you on the aerodynamics? It’s a fantastic partnership between Ron Ayers, who’s spent 50-odd years in the aerodynamics business and has this massive bank of experience, and us here with the latest computational modelling techniques. Quite often, we start off with a design, an initial concept of the car, I’ll go away and analyze in CFD and come back with a set of data that as a team (Ron Ayers, John Piper, other designers — mostly based at the University of the West of Have you done any wind tunnel (scale or England in Bristol — and myself) we study and full-size) testing? No, we haven’t. Back in the early ‘90s, Ron try to understand. Quite often Ron will suggest Ayers (Chief of Aerodynamics) — who came a tweak based on his experience. We then try it in CFD and 95 percent from the old school of aerodynamics and of the time was pretty suspicious of what CFD could it turns out that do — set the Thrust SSC team a the tweak was worth challenge to trying. Even with the best m o d e l technology in the world there’s no a rocket substitute for experience. sledge test. The Are there additional challenges beyond University did the modelling, he did the test and he Thrust SSC in going from Mach 1 to 1.3? stunned himself with the level of agreement One of the key things we learned from Thrust between the two sets of data. He basically SSC was this whole issue of spray drag, that entraining dust into the airflow is a massive convinced himself that we can trust CFD. In terms of validating what we’re doing, that factor. If you compare this car to Thrust, it effectively happens when we get to the desert. looks completely different: Thrust had a very What we’re not going to do, just because we large cross-sectional area which meant that believe we’ve got a 1000 mph car, is to tell there was a lot of surface for high-speed dust Andy: “Off you go, foot to the floor.” We’re to impinge upon. We had to get our weight going to slowly increase the speed of the car down — Bloodhound is about half the weight over a prolonged period of time and at each of Thrust SSC — and the thrust up — which is stage, come back and compare data from the why we realized straight away that we needed car with the CFD models. If at any point the something with more thrust per weight than a two sets of data diverge, then before we press jet engine. That’s why we have a rocket, which any further up the speed regime we need to in turn affects the shape the car needs to be as a rocket is long and thin. understand why. like that but the reality is that, however good our CFD models are, we’re not going to know how right we are until we get there. One of the reasons we call this an Engineering Adventure is because all the numbers stack in our favour — it looks like we can do this, we believe we can design a safe vehicle that will do the job — the reality is that we won’t know until we go to the desert and compare data from the car with our models.
What aero considerations are there concerning the turbofan air intake in going supersonic? A jet engine wants to receive air in the compressor phase at about Mach 0.6-0.7. The car will be going up to speeds more than double that. The job of the intake duct is to slow the air down so that it’s pressurised in as effective a way as possible. We’ve worked with the engine manufacturers themselves to help us design this duct, from the start of the cockpit, all the way to the area of the face of the intake duct, through the expansion ratio through the duct itself — all that is being used to deliver a good quality of air to the jet engine.
Do you have any active aero devices on the vehicle (e.g. to change drag, centre of pressure, downforce at different speeds)? In terms of controlling the vertical forces on the car, the winglets on the front of the car are moveable surfaces. But “... Above Mach 0.3 the lateral they’re not going to be controlled by the driver, they’ll be aerodynamic forces that the controlled by computer. Any of these changes we’ve tried front wheels generate far to design out but are there in the end will get trimmed out outweigh the traction force by those winglets. between the wheel and the In terms of directional stability, it’s actually in the ground.” rules of the Land Speed Record that you’re not allowed to use any aerodynamic steering devices — it’s a completely fixed-fin, no-rudder device. But we’ve done a lot of work to establish how much aerodynamic steering we get off the front wheels. Obviously if you move the front wheels travelling at those speeds they’re going to generate some kind of lateral forces. We’ve shown that above Mach 0.3 the lateral aerodynamic forces that those front wheel generate far outweigh the traction force between the wheel and the ground but the car is steered by these front wheels.
You consume a massive amount Where are you going to make the record attempt? of fuel during a run. In fact you When this project went live there was a professor of the school of have an 800 bhp V-12 racing “We ... get through an environmental society at Swansea who had this software that could engine, the sole purpose of enormous amount of scan the whole globe for a given type of surface. He came up with a which is to pump fuel to the jet fuel — just under two short list of about 30 locations based on the criteria we specified — and oxidant to the rocket. What tonnes — in a run.” like no vegetation, flat, at least 10 miles long, and so on. We’re now unique challenges have arisen down to a list of about seven. Top of the list, at the moment, is South Africa, a as a result? place called Verneuk Pan. We always want our lateral centre of pressure The final choice will depend a lot on when the car’s construction is finished in to be behind the centre of gravity — that’s the 2010, determining whether we go to the South or North Hemisphere. basic requirement to have a directionally stable vehicle. But we do get through an enormous Was altitude a consideration? amount of fuel — just under two tonnes — in There are tradeoffs. The higher you go, the lower your drag. The higher you go, a run. The fuel tanks are placed as close to the less efficient your jet engine is. It’s hard to say what the optimum altitude is the centre of gravity as possible so that as you but we can believe the car can do the job pretty much whatever the altitude. We throw away this weight, the centre of gravity even considered a desert in Bolivia at 10,000 feet and when we ran the figures is moves as little as possible. With our current the car ran okay. layout we think the CG moves about 30 cm. between full and empty tanks. Which we can When do you expect to carry out the record attempt? live with — we are confident we can keep Providing we get the sponsorship money we’re anticipating, we expect to start the centre of pressure where allows the car to building the car this summer and finish the build in Spring 2010. Then we’ll start remain drivable. doing some low-speed (250-300 mph) runway testing in the UK. I expect that, all going well, by Summer 2010 we’ll be on location starting our high-speed runs. What controls does the driver have? Ideally, we’ll do three desert visits, the first to 800 mph, the second to 900 mph He has: a steering wheel (connected to the and the third to 1000 mph. Each time we’ll come back, analyze all the data and front wheels); a throttle (on the jet engine); and if necessary modify the car. controls for the rocket, the air brakes (at the rear of the car) and the three-stage parachute. Roughly how many test runs will you run to check and evolve the aerodynamics and systems of the vehicle before the record attempt itself? Can you control the rocket? We’re anticipating we’d do in the region of 50 or 60 runs per visit. That may You can terminate it. It’s a hybrid rocket, increase if we’re in South Africa because the location has a much wider weather the largest of its type ever developed in window than, say, Black Rock in the United States. Britain, we believe. Liquid oxidant (hydrogen peroxide) gets pumped into the rocket where, CONTACT once a certain temperature is reached, the Follow Bloodhound SSC at www.bloodhoundssc.com solid grade fuel ignites. 26
WIND TUNNEL INTERNATIONAL | 2009
Optimizing wind tunnels and CFD allocation
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Pratt & Miller Engineering (PME) has specialized in reducing product development time and cost by careful selection of alternative development methods to best address specific product
2009 | WIND TUNNEL INTERNATIONAL
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distance Adams Golf turned the business of golf design on its head in 2008 when it introduced the aerodynamically designed Speedline driver to critical acclaim and Tom Watson rewrote history using it in his memorable second place in Julyâ€™s British Open Tournament at Turnberry. By Scott Burnett, Adams Golf Ltd, Plano, Tex., and Michael R. Mendenhall, Nielsen Engineering & Research, Santa Clara, Cal. Tom Watson and his Speedline driver, which was a key enabler in his incredible second place at The Open, Turnberry in Scotland.
WIND TUNNEL INTERNATIONAL | 2009
sk most golf club designers what the ultimate goal of
a good driver — the club used to blast off the tee on everything but the shortest of holes — and the answer is: Distance, distance and (more) distance.
Golf club drivers have dramatically increased in size in recent years as a result of developments in material and manufacturing technology, always with an eye on the ultimate goal of distance. The performance of golf club driver heads has been studied extensively by the golf industry and has led to design targets for certain physical properties of the club head. For example, recently manufacturers have been targeting a high rotational moment of inertia (MOI) of the club head to decrease the energy loss for off center impacts. The rapid increase in size led the United States Golf Association to establish design constraints incorporated into the rules governing golf equipment. These constraints include: • A displaced volume limit of 460cc • A notional “box” with dimensions of 5 x 5 x 2.875 in. within which the club head must fit • And a moment of Inertia limit about the vertical axis of 5900 kg mm2 The major challenge faced by designers is that a 460 cc driver head cannot be easily designed to hit the dimensional and MOI limit without resorting to unusual club head shapes. Moreover, during a golfer’s swing the club head is exposed to wide variations in wind speed and orientation. During the first part of arm rotation, the club is plowing the air with the heel of the club, from which it is rotated rapidly to impact, During that time, the air stream rotates from the heel of the club to the face plane — a total orientation change of 90 deg. Additionally, as the club is moving thru these orientations, it also increases in velocity from zero to over 100 mph — more with professional golfers. Since its introduction, the Speedline driver has been in the bag of multiple winners on the LPGA tour and on the Champions tour with Bernard Langer (this picture and right)
2009 | WIND TUNNEL INTERNATIONAL
After extensive study of the performance ramifications of driver heads near these maximum dimensions, one extremely important and somewhat unexpected performance issue was identified. By having golfers swing different driver designs and measuring the club head speed they obtained just before ball impact, it was determined that the external shape of the driver head had a significant influence on the measured club head speed. Broadly speaking, higher clubhead speeds result in higher ball speeds, which in turn lead to longer drives. With this in mind, an initial design was conceived to conform to the dimensional and MOI rules and the prototype (called the “Bullet”) was typical in having a somewhat unusual head shape. While the design did have some desirable properties, player testing revealed that golfers’ maximum club head speeds were reduced with this club by approximately three percent versus a “traditionally” shaped 460 cc driver — a major disadvantage off the tee. A generally accepted rule of thumb is that, for instance, a three-percent drop in club head speed leads to a three-percent reduction in total drive distance. This result was unexpected and led to a study of the aerodynamics of golf club heads both in “During (the swing), the air the wind tunnel and stream rotates from the heel using computational of the club to the face plane — fluid dynamics a total orientation change of (CFD) analysis. It 90 deg. ... and (the club) also led to the Adams increases in velocity from Speedline driver, now zero to 100 mph” in production. An extensive series of wind tunnel tests were conducted at the Oran W. Nicks Low Speed Wind Tunnel at Texas A&M University. The driver heads were mounted on a short portion of a shaft connected to a balance to measure forces and moments. The heads could 31
â€œA large number of ... driver heads was selected for testing at a range of flow velocities representative of speeds attainable by accomplished golfers.â€?
Validation by CFD To validate the design and better understand the drag characteristics and sources of drag on typical driver heads, a computational fluid dynamics (CFD) study was also conducted. Using the NASA-developed OVERFLOW code, the same analysis process that has been successfully used for the design and analysis of aircraft, missiles, rockets and other vehicles was applied to Bullet and Speedline driver head configurations. The objective of this analysis was to understand the relationship between a driverâ€™s design and its aerodynamic drag and apply this knowledge to the design of effective drivers with low drag.
be rotated to change both the lie angle and the flow angle at the head, and the driver heads were positioned in the free stream out of ground effect. A large number of commercial and prototype driver heads was selected for testing at a range of flow velocities representative of speeds attainable by a ccomplished golfers. Because of the complex design and use constraints, initial wind tunnel and CFD analyses was conducted at a variety of orientations and speeds. It was found focusing
computational grid was developed for the driver heads having approximately 15-million elements. Where possible, all the details of the surface cavities were included in the computational model, and the short section of the shaft used to mount the head in the wind tunnel was included in the grid. The viscous Navier-Stokes equations were solved for the turbulent flow over the head using the Menter turbulence model. The solutions were run to convergence, a process which generally required several thousand iterations. The technical approach followed was first to model a driver head for which wind tunnel data were available, the Adams Bullet prototype configuration in this case. The CFD results for lift and drag forces were compared with the data over the entire range of flow angles for validation purposes to build confidence in the analysis procedure.
As with traditional aerodynamic analyses, a detailed structured The comparison of measured and predicted drag forces is shown in Figure A for the driver at a typical lie angle at a speed of 100 mph. The interesting result of this comparison is that the predicted character of the drag on the driver is in reasonable agreement with the measured drag over the entire range of flow angles. The maximum drag on the head, occurring near the 90-degree orientation angle, is also in good agreement. Although not shown here, the measured and predicted lift forces on the driver head are in similar agreement. These results provide some confidence for using CFD to understand the source of the drag, and further, to use CFD to analyze the drag characteristics of driver configurations for which no measurements are available. Similar CFD techniques were applied to the Adams Speedline driver
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on 100 mph gave results which correlated well to the golfer swingspeed measurement data. As a result of these tests a refined design which it was thought would lower the aerodynamic drag and still produce a high rotational moment of inertia was developed. The shape differences are quite obvious when compared to the Bullet prototype and it was this design which became the Speedline driver in production. Among all the club heads tested, a small sub-set is presented here to compare with the Speedline, chosen because they showed interesting aerodynamic drag characteristics in the player tests and the wind tunnel testing. In addition, these driver heads are representative of the range of clubs currently sold in the market place. The Ping G10 is head and a comparison of drag between the Bullet and Speedline drivers (head alone) is shown in Figure B. The CFD results on these two heads can be used to identify the different flow characteristics which produce lower drag on the Speedline design. For instance, a comparison of the streamlines and flow-field pressure coefficient in the face-on wind orientation (90-degree orientation) conducted at 100 mph (Figure C) illustrates the large region of separated flow on the upper back side of the higher-drag Bullet configuration. The flow in the same region of the lower-drag Speedline club has a much smaller separated region. The extent of the separated region is an important factor in the drag on the head because of the low pressure in this region. A view of the surface pressure coefficient on the two heads is shown in Figure D. Using the surface pressure coefficients, it is possible to analyze the contribution of different regions of the club head to the total drag of the club and the way shaping could be used to improve drag characteristics in future designs. 1. There is a high-pressure area on the club face. This is an expected result since frontal area is known to be critical in aerodynamic drag. Reducing the face area and the frontal cross sectional area for the various orientations would result in reduced drag but may be unacceptable because of other functional requirements. 2. The low-pressure area (in blue in Fig. D) around the perimeter of the face is acting on surfaces normal to the direction of travel which means this phenomenon is actually decreasing the drag on the club. This portion of a club head can be designed to increase
Actual club head speed tests with golfers confirmed the wind tunnel and CFD findings
representative of smaller dimension “traditionally shaped” 460 cc club heads and shows relatively low aerodynamic drag. The Tour Burner and Cobra F-Speed are typical of larger dimension “unusually shaped” club heads, and both show a dramatic increase in aerodynamic drag. The tests measured aerodynamic drag at 100 mph as the club head was rotated from heel-on wind (0-degree) to flow directly at the face (90-degree orientation). The measured aerodynamic test results show the dramatic increase in drag as the flow approaches the 90-degree orientation for the Cobra L5V and Taylormade Tour Burner drivers. The Speedline Prototype exhibits low drag characteristics at all flow orientations. Although the wind tunnel tests showed a measurable difference in terms of aerodynamic drag for different driver designs, there was still a question whether this translates to club head speed. Golfer tests with the same four club heads tested in the wind tunnel program show that a decrease in average club speed is associated with an increase in measured aerodynamic drag, as shown in the accompanying chart. Based on extensive player testing, wind tunnel testing and CFD analysis, it is reasonable to conclude that aerodynamics has become a critical design consideration for today’s large-dimension 460 cc drivers. The aerodynamic drag increase for a poor aerodynamic design can be so large (approximately twice what a well-designed driver experiences) it decreases the club head speed and driving distance golfers are able to achieve.
the size of this low-pressure area surrounding the face without increasing frontal area to contribute to lower drag. 3. Streamline reversal on the crown and the associated lowpressure area on the back surfaces of the club head are important drag contributors. The flow over the crown is not attached to the crown for the extreme-dimension driver because of the rapid fall off of the crown. This creates a large lowpressure area on the crown and the back of the head causing an increase in drag. Any head design which keeps the flow attached to the crown or minimizes the aft facing low-pressure surfaces will decrease this drag source.
CFD, validated with wind tunnel data, has been shown to be a useful tool to understand the fluid mechanics of the flow around modern golf drivers, and it provides a reliable design tool to optimize the head shape for aerodynamic considerations. As in other industries, CFD can be used to filter driver designs to reduce the number of configurations taken to the prototype and testing phase and contribute effectively to the development of the final design. 2009 | WIND TUNNEL INTERNATIONAL
Actual club head speed tests with golfers confirmed the wind tunnel and CFD findings
As well as Watson’s spectacular success, the Speedline driver has been in the bag during six tournament wins since its release, four on the Champions Tour (three of which came in the hands of Bernhard Langer) and two on the Ladies PGA Tour. 33
UNIVERSITY OF AUCKLAND
New Zealand’s America’s Cup
Team New Zealand’s emphatic victory in the 1995 America’s Cup and successful defence in 2000 was largely attributed by experts to the team yacht’s superior downwind performance. This was a result of improved simulation carried out in the Twisted Flow Wind Tunnel at the University of Auckland, which was originally designed and built by the University of Auckland, North Sails New Zealand and Team New Zealand specifically for investigating the performance of downwind sails used in the 1995 America’s Cup. It is used for testing yacht sails by modelling the full scale conditions as accurately as possible. By David Le Pelley, Yacht Research Unit, Mechanical Engineering Department, The University of Auckland 34
nlike most other to be confused with wind shear,
for ms of w ind tunnel testing, the aim is to simulate a yacht moving at a significant angle to the true wind direction through the atmospheric boundary layer at a comparable speed to the wind speed. This introduces a change in not only apparent wind speed (as seen by the yacht) but apparent wind direction with height. This apparent wind direction can vary by as much as 40 degrees between the foot of the mast and the mast tip. This wind twist is not
which can be present in the onset flow but is not a result of the boat’s motion. Depending on the velocity gradient, it is even possible to end up with apparent head winds at deck level when sailing downwind, as most of the driving force is produced by the stronger winds near the masthead. Quite different setups are required for testing upwind and downwind sails (Figure 1). Downwind (or offwind), where the boat speed can be almost twice the wind speed, the apparent velocity profile is much more severe than
WIND TUNNEL INTERNATIONAL | 2009
UNIVERSITY OF AUCKLAND
“In yachts, wind twist can cause the apparent wind direction to vary by as much as 40 degrees between the foot of the mast and the mast tip ... it is even possible to end up with apparent head winds at deck level when sailing downwind” the true wind profile and the apparent twist is therefore large. The turbulence intensities in the apparent wind reach quite high levels (up to 20%). All of the simulations are referenced to a 10m height, and it is not uncommon for a high performance yacht sailing at 140 degrees to the true wind to have an apparent wind angle of 45 degrees which is modelled in the wind tunnel. When sailing upwind, a large component of the boat speed is into the true wind direction which suppresses the apparent velocity gradient and so minimises the twist profile. The turbulent intensity is similarly less. The vertical wind velocity profile is modelled by placing bars at various heights in the flow and roughness elements on the floor of the tunnel upstream of the test
section to slow the flow near the floor. The horizontal wind twist is achieved by twisting flexible vanes upstream of the model. However, these apparent speed and twist profiles will change for every simulated true wind angle and boat speed combination, so in practice a range of settings needs to be developed before testing. These are measured using a 4-hole Cobra probe mounted on a vertical traversing rig. This determines the horizontal flow angles, wind speeds and most importantly the pressure factor between the reference pitot tube upstream and the model scale at 10m height. The yacht model is constructed as accurately as possible. This is a very important step as the flow behaviour over and around the hull can have a significant effect
2009 | WIND TUNNEL INTERNATIONAL
Scale model undergoing downwind and upwind testing in the University of Auckland’s Twisted Flow Wind Tunnel
on the aerodynamic forces. Tests have shown that around 10-15% of the overall side force is carried by the hull when sailing upwind. The foredeck shape, for example, is critical as small sheeting changes alter the degree to which the genoa sail is sealed to the deck. Once the foot is eased away from the deck edge, the pressure distribution over the hull and sail changes and there is a subsequent reduction in lift efficiency. Model sails are designed to be as light and flexible as possible whilst retaining their shape in the wind tunnel. Model sail dimensions are typically accurate to around 1mm which equates to an acceptably small difference at full scale (typically around 1:15 scale factor), enabling very small variations in sail shape to be tested with confidence. Obviously, it is not possible to match Reynolds number in the wind tunnel for this type of testing — that would require a wind speed of about 150m/s. Even though the sail performance seems to be largely driven 35
FEATURE UNIVERSITY OF AUCKLAND
“The wind tunnel allows customers to trial several sail concepts at a fraction of the cost of full scale sails … ultimately providing better sails to their clients”
Model of 100-foot super-yacht at 1:20 scale showing heel motor, angle sensor and onboard winch system
Sail selection chart being developed in the wind tunnel
by the amount of attached flow and by delaying separation on the offwind sails, the simulation in the wind tunnel seems to be quite reasonable, both in terms of pressure distributions compared to full scale and with overall force predictions. What is much more important is that the sail inflation is correct. If this is not maintained, the sail flies in the wrong position and sets up an incorrect flow field, which in turn alters its shape. This requires a wind speed based on a pressure scaling approach which is determined by the weight of cloth used, and is fortunately a much more realistic 2-5 m/s. This provides enough force resolution without stretching the sails or overloading the model. The model is installed in the
wind tunnel and mounted on a 6-component force balance positioned beneath a turntable. The trough that the model sits in is filled with water which provides a perfect seal around the hull without transferring any forces to the model. The model is equipped with remote-control electric winches to enable the sails to be trimmed in exactly the same way as they are at full scale. Professional sailors are often used to trim the sails throughout the tests, and this also gives them the chance to have a look at the flying shape in the tunnel at an early stage and add input to the design process. A range of remotecontrolled cameras around the test section captures sail shapes from several angles. At this stage the yacht’s hydrodynamic parameters (either from CFD or towing tank results) are loaded into the Real-Time Velocity Prediction Programme (RT-VPP). This system has been developed by the University of Auckland to improve the speed and accuracy of the testing, and make it more intuitive for the sail trimmers. It works like this: the force balance in the wind tunnel measures the aerodynamic forces and moments acting on the boat. For a particular true wind speed, the RT-VPP scales up the wind tunnel forces and balances them against the hydrodynamic forces, producing the correct equilibrium values of boat speed, heel angle, leeway and rudder angle every second. A command is then sent to a heel motor which heels the model over in the tunnel to the required angle. If the sail is sheeted in further and the aerodynamic roll moment increases, the required heel angle for equilibrium changes and so the model heels over more in the
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UNIVERSITY OF AUCKLAND
Visual sail tracking system in use on downwind gennaker
tunnel. The advantage of this system is that heel and depowering effects can be determined directly in the wind tunnel. The yacht behaves exactly as it would at full scale — even effects such as balance and rudder stall can be looked at in real time using this system. Typically, the sail is tested at apparent wind angle increments of 10° over its full range and 3-4 different true wind speeds are simulated at each apparent wind angle. Once a suitable trim has been achieved for a particular condition, the forces are averaged over a period of around 60s. This length of time is required as the behaviour of downwind sails is essentially unsteady — being only a thin membrane they tend to oscillate due to the highly turbulent onset flow, a phenomenon that occurs at full scale in a similar way. The RT-VPP enables a sail-selection chart to be developed using either boat speed or driving force. A typical sail crossover chart under development in the wind tunnel for a high performance racing yacht, where each candidate sail is represented by a different colour surface. The wind tunnel driving force, measured at a fixed wind speed, drops off at the higher simulated true wind speeds due to the boat heeling and the sails being depowered. The data analysis and plotting software is linked to the data acquisition software and RT-VPP such that the plot is automatically created for each sail. This instantly shows up any poor sail trim conditions and the run can be repeated. An interesting feature is that, if there is a non-fair surface developing, it is invariably the low points which are “incorrect” as the resolution, accuracy and repeatability of the wind tunnel system is usually much better than the ability of the sail trimmer, at least at the start of a testing session! Recent advances include the use of a boat-mounted visual system to capture and analyse sail trim to assist the trimmer. Using this system, the Yacht Research Unit has carried out testing for many of the major high performance yachts built in the last decade, and it provides a significant advantage over other competing wind tunnels. One of the key clients is North Sails New Zealand, whose General manager Richard Bicknell says that the advantage of the wind tunnel is that ultimately it allows them to provide better sails to the client. They can trial several concepts at a fraction of the cost of full scale sails and make more confident design decisions based on the data they get out of the tunnel. CONTACT David Le Pelley, Pelley The University of Auckland E-mail: firstname.lastname@example.org
2009 | WIND TUNNEL INTERNATIONAL
Next â€“ The Moon. Then Mars? Four decades after the Apollo program met its primary goal, NASA is working towards returning to the Moon. New efficiencies, primarily through the application of modern technologies, including aerodynamic studies, assure a more efficient and less costly approach. By Clifford J. Obara, NASA Langley Research Center, Ground Facilities and Testing Directorate 38
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Astronaut Neil Armstrong works at the lunar excursion module.
A concept image shows the Ares I crew launch vehicle during ascent. © NASA/Marshall Space Flight Center
his year marks the 40th anniversary of the successful flight of
Apollo 11 and the first human steps on the surface of the moon. Millions of Americans and people across the world were glued to their television sets as Neil Armstrong first stepped out of the lunar excursion module and pronounced “one small step for man, one giant leap for mankind.” Apollo 11 remains today one the most significant accomplishments in the history of the National Aeronautics and Space Administration (NASA).
© NASA/Johnson Space Center
2009 | WIND TUNNEL INTERNATIONAL
Now, forty years later, NASA is embarking on a space adventure to return to the moon and venture beyond the bounds of previous manned space flight. In 2004, then President George W. Bush announced a new vision for space exploration: “Inspired by all that has come before, and guided by clear objectives, today we set a new course for America’s space program. We will give NASA a new focus and vision for future exploration. We will build new ships to carry man forward into the universe, to gain a new foothold on the moon, and to prepare for new journeys to worlds beyond our own.” Unlike the resulting Apollo program that was undertaken following President John F. Kennedy’s speech in 1961, the new exploration vision has much broader 39
“This will not be a bottom-up approach, as much of the technologies from the Apollo and Shuttle programs will be used to help develop a more economical and dependable spacecraft.” goals with less emphasis on getting it done quickly or the availability of nearly unlimited resources. Nonetheless, the new vision has brought a clear focus on what NASA is to do in the coming decades for space exploration. The Constellation Program is the start to this vision by providing two new space exploration vehicles to access the International Space Station, return man to the moon and visit other far reaching worlds. This will not be a bottom-up approach, as much of the technologies from the Apollo and Shuttle programs will be used to help develop a more economical and dependable spacecraft. Advancements in computer technology, material processing, and experimental techniques will lead to a more efficient and lighter space vehicle. There are four primary components to the Constellation Program. The Ares I, crew launch vehicle is the rocket that will launch the astronauts into orbit. It is an in-line, twostage configuration topped by the vehicle that the astronauts will ride in, the Orion crew exploration vehicle, and the launch abort system. In addition to the vehicle’s primary mission of carrying crews of four to 40
ABOVE: This artist’s rendering represents a concept of the Orion crew exploration vehicle in lunar orbit. (Depicts obsolete configuration.)
© Lockheed Martin Corp.
A concept image shows the Ares V cargo launch vehicle.
© NASA/Marshall Space Flight Center
six astronauts to Earth orbit, Ares I may also use its 25-ton payload capacity to deliver resources and supplies to the International Space Station or to “park” payloads in orbit for retrieval by other spacecraft bound for the moon or other destinations. The versatile Ares V rocket will
be used to launch heavy cargo into low-earth orbit. It can carry nearly 414,000 pounds of cargo including the lunar lander and materials for establishing a base on the moon. The Altair vehicle is the lunar lander and outpost that will be used to get the astronauts to the moon surface. Altair will be
WIND TUNNEL INTERNATIONAL | 2009
“Unfortunately, the available wind tunnels do not meet all of the flight conditions expected. For Mach numbers less than five, the available wind-tunnels are only capable of 10 to 100 times lower Reynolds numbers.”
ABOVE: Three crew members work in the area of their lunar lander on the lunar surface in this NASA artist’s rendering.
© NASA/Langley Research Center
capable of landing four astronauts on the moon, providing life support and a base for weeklong initial surface-exploration missions and returning the crew to the Orion spacecraft that will bring them home to Earth. This article will focus on the aerodynamic and aero-acoustic testing of the Ares I and Orion vehicles. The Ares V program will follow a similar rigorous research development effort as the Ares I, adapting as many lessons learned
from the earlier Ares I testing. In terms of aerodynamic analysis and wind-tunnel testing, there are two primary environments that are of interest in the development of the Ares and Orion vehicles. The first environment is the atmospheric entry, which encompasses the re-entry of the Orion vehicle on its return to earth. The second is the ascent abort separation environment, starting from pad abort and going to hypersonic abort. Since these
2009 | WIND TUNNEL INTERNATIONAL
Nominal flight Reynolds number and wind-tunnel operating ranges for the Ares I crew launch vehicle.
environments encompass the entire speed regime from subsonic (pad abort) to hypersonic (upper atmosphere jettison or abort and reentry), a large selection of wind tunnels are being utilized to determine the aerodynamic characteristics of these vehicles. This includes a minimum of 18 wind-tunnels from both government and commercial entities. Studies are being conducted across most phases of the flight envelope including ground wind loads, transition from pad to ascent, stack ascent, stage separation, first stage re-entry, and upper stage. Unfortunately, the available wind tunnels do not meet all of the flight conditions expected. For Mach numbers less than five, the available wind-tunnels are only capable of 10 to 100 times lower Reynolds numbers. It is only at Mach five and above that actual flight Reynolds numbers can be matched in the wind tunnel. For the subsonic to supersonic Mach numbers, testing is done at various wind tunnels to determine Reynolds number trends. Corrections are then applied for the flight conditions with the aid of computational fluid dynamics (CFD). The importance of the wind-tunnel tests cannot be underestimated as they will provide the validation for the CFD 41
© NASA/Langley Research Center
Virtual diagnostics interface image of the Ares I showing computational predictions superimposed over experimental image data in real time.
begin with the overall physical size and shape of the vehicle. The length and slenderness limits the model scale that will fit in the wind tunnel without significant blockage effects that can alter the measured performance. The slenderness also affects model support and balance loads since the center of gravity is a relatively long distance from the sting attachment point. The model scale can also limit the range of angle-of-attack and sideslip capability. Other model features that are affected by the model scale include the ability to have built-in or on-board instrumentation such as pressure taps and angle-of-attack © NASA measurement devices. Smaller scale models Pressure sensitive paint image of Orion crew exploration vehicle. make it more difficult to model smaller features on the model itself such as vents, rollcontrol jets and other protuberances. To overcome these challenges, a variety of tests is being conducted by using the same model in different wind tunnels or by comparing different scale models in the same wind tunnel. The strength in doing these © NASA repeat tests will be a Artist concept of the Orion crew exploration vehicle reentry to earth’s atmosphere. reduced uncertainty codes which in turn will make the necessary in the experimental data as well as a better predictions for flight conditions. A case in validation of the CFD predictions. In addition, point is the National Transonic Facility which advanced measurement techniques are being has the highest Reynolds number capability of used such as pressure sensitive paint and any of the transonic tunnels, providing better the virtual diagnostics interface for merging validation of the CFD predictions. Great care CFD and experimental results in real time. A is being taken to ensure the quality of the CFD solution is mapped onto the computer wind-tunnel data both in repeatability and generated model and then super-imposed with in understanding the uncertainty of the data. real-time measured data such as a focusing The challenges to the Ares research program Schlieren image or actual pressure tap data. 42
The researcher then has the ability to make real-time decisions as to the quality of the data and where next to go. For the Orion program and to a great extent the Ares program, the wind-tunnel test requirements include static aerodynamics, buffet, dynamic stability and aero-acoustic testing. The primary purpose of the aeroacoustic data is to measure the acoustic environment which will be imposed on the astronauts and the control instrumentation of the vehicle during nominal ascent and firststage re-entry. The aerodynamic data supports the guidance, navigation, and control aspects of the vehicle during nominal entry and descent. It will also be used to test the Orion flight control system against the expected flight behavior by directly supporting the flight tests. Another major aspect of the wind-tunnel tests is the study of the launch aborts from pad to Mach 7 plus. The database is being populated with static aerodynamic and dynamic stability data along with increments due to the proximity to the Ares I launch vehicle. In addition, abort motor jet interactions with the crew module aerodynamics are being studied. Early results to characterize the separation characteristics between the launch abort vehicle, which comprises the crew module and the launch abort system, had already concluded that the aerodynamic loads were different than the launch abort vehicle by itself. Previous Apollo data showed an increase in the axial force during separation. Generally, the abort motor thrust level is set by the transonic/ maximum drag abort initiation and downrange requirement for pad abort. Current separation wind-tunnel tests indicate that the thrust can be reduced from the current thrust-to-weight ratio of 15. Unique to the Orion program is the aerothermodynamic study of the vehicle re-entry to earth’s atmosphere. Here, the philosophy is to rely primarily on computational studies with wind tunnel experiments providing validation for targeted flow conditions. Apollo flight data is also used to compare to the CFD results in order to develop “best practices” and uncertainty assessments. While one may perceive a step back in time to the Apollo era, the new class of space vehicle being developed in the nation’s wind-tunnels will be a much more efficient spacecraft that will have a broader capability of taking man beyond the reaches of the moon while still maintaining support of the International Space Station. CONTACT Clifford J Obara, NASA E-mail: email@example.com WIND TUNNEL INTERNATIONAL | 2009
18 0 m p h w i t h o u t m o v i n g a n i n c h
Take cutting-edge wind tunnel technology. Add a 180 mph rolling road. And build in the best in precision data acquisition capabilities. When we created the worldâ€™s first and finest commercially available full-scale testing environment of its kind, we did much more than create a new wind tunnel. We created a new standard in aerodynamics.
w i n d s h e a r i n c .c o m
When LM Glasfiber commissioned its new wind tunnel in 2006, the expected benefits claimed by the company appeared quite modest, while significant. But latest research in the tunnel, plus the introduction of the first blade with profiles developed in the tunnel, show cause for considerably greater optimism. Rex Greenslade reports.
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LM Glasfiber’s wind tunnel is first customdesigned for blade development
M G l a s f i b e r is t he world’s leading supplier of rotor blades for wind turbines, and the only supplier that operates on a global basis. So it was highly appropriate that when, in June 2006, it put into operation its wind tunnel in Lunderskov, Helge Sander, Denmark, it was also able to claim that it was the world’s first wind tunnel custom-designed for research and testing in this industry. Representing an investment of DKK 25 million (approx. $4.7 million), the tunnel’s stated goal was to provide new know-how to ensure that tomorrow’s wind turbines can continue to generate more and more power and, by doing so, present LM Glasfiber with a significant competitive advantage. The wind tunnel gives LM Glasfiber’s team of aerodynamicists and engineers a world-exclusive opportunity to conduct tests, 24 hours a day, 365 days a year, to develop the optimum aerodynamic blade design. During the past 20 years, the capacity of wind turbines has doubled about every four years. As a result, over the same period, the price of wind power has been reduced by approximately 80 percent. For instance, a wind turbine with three of LM Glasfiber’s largest blades is able to generate power sufficient to cover the annual consumption of 5,000 households. Just ten years ago, four of the most advanced turbines at the time were required to cover the same power consumption. Already in 2006, though, LM
Glasfiber was seeing that this rapid pace of change was reaching a plateau. Wind technology had already reached such an advanced stage that decisive new knowledge was required if similar efficiency improvements were to continue to be achieved. ”In fact, efficiency is now so high that we have started to operate with margins when we speak of efficiency,” said Frank V. Nielsen, LM Glasfiber’s R&D Director at the time. ”But the margins are very important. If our blade design can help boost the annual power production by a mere two percent during its 20-year lifetime, it will generate so much more power that, in financial terms, it will offset the financing cost of the wind turbine. We are confident that our new wind tunnel can contribute with the knowhow required for us to achieve this higher efficiency.” The tunnel has a closed return loop, a contraction ratio of 10:1, a honeycomb and turbulence screen help to ensure a high flow quality in the test section and a cooling system to maintain constant temperature conditions. The test section dimensions are 1.35 m width, 2.70 m height and 7 m length. This gives very little blockage and only limited streamline curvature for an airfoil model with a 900 mm chord. Testing confirmed that the designed maximum flow speed of 375 km/hour or Mach 0.3 could be obtained with the 1 MW powered fan. This yields a maximum Reynolds number of more than 6 million for an airfoil model with a chord of 900 mm. A high-accuracy turntable device
2009 | WIND TUNNEL INTERNATIONAL
The wind tunnel’s test section showing high-accuracy turntable
“Margins are very important. If our blade design can help boost the annual power production by a mere two percent ... it will offset the ... cost of the wind turbine.” 1MW fan gives Mach 0.3 maximum
This state-of-the-art rig can test blades of up to 80 metres in length.
any conceivable operation condition that the profile may be subjected to on the blade. By way of example, we have made close to 70 individual tests just to get the complete data basis for one new profile,” explains Peter Fuglsang, Chief Aerodynamicist. On average, about five tests can be carried out per day, which means that the series of tests referred to by Peter Fuglsang takes 14 work days in the wind tunnel, and that’s without counting the data basis documentation. Initially, during the first 10 months of the wind tunnel’s life, the test program focused in particular on the development of new profiles for the blades’ outer half or tip, improvement of existing profiles in the blade root, and optimization of so-called passive aerodynamic devices. As in classis aerodynamic theory, the fluid boundary layer that forms between the fast-moving outer flowing mass holds the airfoil model while an automatic and the fluid resting at the surface of the airfoil is initially traverse system holds a wake rake. In total laminar. At a certain point, the flow becomes unstable and almost 300 sensors are used to characterize small waves form and grow until they eventually break up the airfoil flow including differential pressure at the point of transition. From that point on, the boundary sensors and a load cell system. An automatic layer is turbulent, significantly increasing the frictional data acquisition system allows a high level loss of the airfoil. of uniformity between different tests. The “This may sound a bit Identifying that transition point — at which turbulence results from post processing of all sensors add strange ... but we have sets in — is key and a new state-of-the-art infrared additional 400 values. been working on the camera enables the exact detection of exactly where the The formidable challenges a wind turbine development of a new turbulence is generated in the boundary layer as well as blade engineer must face go beyond size series of profiles with the detailed study of the boundary layer of the airfoils (though the largest LM Glasfiber blade’s low maximum lift.” generally. The new camera takes 30 pictures every second length, at 61.5 m, is about 90 percent of the — corresponding to wingspan of the largest Boeing 747) and shooting video — optimised aerodynamic design (which defines and features the width, thickness and twist of the blade). technology used A wind turbine blade does not have the same by the American aerodynamic efficiency along its entire length. Forces to target fastTowards the root, thick airfoils are used to moving people or enable the blade to bear its own weight. vehicles. The blade is circular at this end, to permit “This may sound mounting on the turbine. These factors have a bit strange,” Peter a negative effect on the blade’s performance Fuglsang comments, as can widely differing wind speeds between “but we have been the lowest and highest elevations a blade’s tip passes through each revolution and variations in overall wind speeds working on the development of a new series of profiles with low maximum lift. With lower maximum lift, we can make the blade longer due to changing weather conditions. The best compromise between optimised air flow and blade strength than when we employ the standard profiles available today. And even must be found, as well as managing the best (generally minimum) if the blade becomes longer, we still keep within the maximum loads applicable to the rest of the turbine’s components. This means that loads on the other parts of the wind turbine. Since its launch in mid-June 2006, LM Glasfiber’s wind tunnel has it is possible to produce more electricity, because the blades cover been bustling, with aerodynamicists taking full advantage of the fact a larger area without increasing the load on, for example, the shaft, gear and hub.” that they now have unlimited access to testing. However, the engineers have not been occupied solely with finding “It takes a lot of trials when you want to define and document new profiles or aerodynamic devices. In order to achieve the best possible lower maximum lift. They have also documented that the new LM result, you have to complete a series of tests that are representative of profiles have a high aerodynamic rate of efficiency and that the
WIND TUNNEL INTERNATIONAL | 2009
profiles are able to withstand dirt and contaminants which may in time settle on the leading edge of the blade. Although wind turbine blades predominantly produce electricity on the outer part, a series of aerodynamic tests have also focused on the profiles in the blade root. The aim here has been a better exploitation of the inner part of the blade with the result of reduced width of LM blades without impairing aerodynamic performance. The width of the inner part of the blade is critical for handling and transport, and improved possibilities of making the blade ‘slimmer’ imply improved possibilities of making longer blades. For several years now, wind turbine blades have benefited from passive aerodynamic devices, socalled vortex generators, small fins mounted in a long row and in a precise pattern and more commonly used particularly on aeroplane wings. On wind turbine blades, they are placed at the innermost of the blade’s upper part with the purpose of optimizing air currents in a specific area of the blade. These fins are mounted opposite each other at a certain angle that causes counter-current eddies in the air flow, delaying the separation of airflow from the surface, i.e. at higher wind speeds. This delays the moment when
The LM 61.5 rotor is fitted to a wind turbine in Brunsbüttel, Germany
Wind power plants of the future are likely to be erected far from shore. This 61.5 metre long blade (the world’s largest) will be installed on a 5 MW wind turbine 25 kms from the shore and in 40 metres water depth.
2009 | WIND TUNNEL INTERNATIONAL
the blades stall and thus lose their capacity to produce power — the lowest part of the blade is thus efficient during a greater part of the turbine’s production time. LM Glasfiber research has shown vortex generators can boost blade performance by four to six percent “It takes an awful lot of tests to find the best possible combination of size, shape and positioning of the vortex generators, and optimizing them in relation to other passive devices increases the complexity of the tests even further,” explains Peter Fuglsang. “However, after a lot of tests, we have established a complete data basis, which enables us to increase efficiency significantly — especially when at the same time, the new LM profiles are employed on the outer half of the blade. Our aim is to achieve a production increase of two percent by means of our improved ‘tailor-made’ aerodynamic design at the same rotor diameter.” But greater benefits can accrue if a larger diameter rotor can be employed. The challenge is to do so within the same load limits. In late 2008, the first fruits of the wind-tunnel effort — the LM 53.2 P blade prototype — was produced. The LM 53.2 P is not only the second largest blade LM Glasfiber’s portfolio
but it is also the first LM blade to be designed with the new fully optimized LM airfoil design. “The LM 53.2 P is a really good example of where we have used our accumulated knowledge and thoroughly tested designs,” says Jesper Madsen, Engineer in the Research department. “The airfoils have enabled us to design a blade at a maximum length while still sticking within the specified loads. Without the new airfoils, it would have been necessary to make a shorter blade and thus the energy production would have been lower.” Series production of the LM 53.2 P prototype is expected to start at the end of 2009. Aerodynamic design rarely follows conventional thought. Iterative design, backed by institutional knowledge and application know-how, is more typical, as enabled by LM Glasfiber’s new wind tunnel. The results already achieved indicate that clear potential exists for efficiency improvements by means of aerodynamic design. LM Glasfiber’s research show the greatest potential — perhaps as much as five percent — is reached when the rotor diameter can be extended without causing a load increase on the other turbine components.
the mother ofâ€Ś While other divisions of Daimler had developed world-class aerodynamic solutions in state-of-the-art test facilities, Freightliner had no comparable means of carrying out similar development on its North American trucks. A different, very unconventional solution was needed, as Matthew Markstaller explains.
s part of Daimler since 1982, in many ways. One thing we have been
Daimler Trucks North America LLC (DTNA, manufacturers of Freightliner trucks) has had access to much of the technology and expertise of the parent company and its other divisions. Over the years, we have leveraged these resources 48
familiar with (and envious of) is the worldleading position of the Mercedes-Benz passenger-car division in aerodynamic development. Thei r w i nd-t u n nel development methodologies, expertise and techniques are truly world-class and have been developed over many decades.
In comparison, aerodynamic development on heavy-duty vehicles in the United States, has been very limited, and generally frustrated by the lack of equivalent resources. This simply came down to the fact that the production numbers of heavy-duty vehicles could not justify equivalent wind-tunnel development programs that lasted hundreds of hours, or finance a wind tunnel facility that would accommodate a truck. While Chrysler, our sister company at the time, completed a fullscale automotive tunnel earlier this decade, at a cost of more than $30 million, yet not nearly large enough to accommodate a Freightliner truck, we at DTNA had to admire from afar. But necessity is the mother of invention, as they say, and we realized that we had to find a way to apply these aerodynamic development techniques to Freightliner vehicles. We understood that if we could come up with a facility, we could make substantial progress very quickly â€” by applying 30 WIND TUNNEL INTERNATIONAL | 2009
The Innovation Truck, developed at the DTNA wind tunnel, takes Freightliner Trucks’ most aerodynamic solution – the Cascadia™ – and adds a sampling of cuttingedge advancements that will further enhance fuel economy. Its aerodynamics reflect particular attention to reduced drag, with the addition of rear wheel fairings to smooth the airflow around the rear wheels, underbody panels that smooth air flow under the chassis and a front air splitter incorporated into the front bumper to pass air around the truck. The Innovation Truck also replaces the mirrors with side view cameras to further reduce drag. Together these enhancements improve the airflow over, under, and around the vehicle – resulting in further fuel savings.
years of automotive experience and lessons learned with automobiles to our heavy duty truck design. We considered a scale-model facility first but a couple of considerations mandated a full scale facility: Scale models make it difficult to produce the level of detail needed to understand intricacies of external and internal airflows, and then optimize those small details while developing the vehicle; and, in contrast with automobiles, trucks are quite custom in nature, with customers able to select various cab configurations, drivetrain components, and a myriad of options, and even down to the wheelbase, the result is that each customers vehicles are different from the next. We wanted to be able to take many vehicle “We understood that if we could configurations, and even come up with a facility, we could bring customer vehicles into make substantial progress very the tunnel for aerodynamic quickly — by applying 30 years optimization. It would be quite of automotive experience and lessons learned with automobiles impractical to build a scale model of every possible vehicle to our heavy duty truck design.” we needed to test.
Cascadia development model undergoing water soiling tests, note fluorescent “rain”, and transparent hood used for underhood flow visualization.
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SOURCE: DAILMER TRUCKS NORTH AMERICA Wind Tunnel Schematic, drawn by The Oregonian © 2008 The Oregonian. All rights reserved. Reprinted with permission.
When we finally accepted that we would need a fullscale tunnel, and that our business case would justify an order of magnitude less investment than a traditional wind tunnel, we understood that we would have to throw out all the traditional assumptions of what a wind tunnel is, and re-invent it. We redefined what we needed to accomplish: • Present a repeatable, road representative, airflow over a tractor/truck. • Provide maximum air speed of 65 mph. These new parameters allowed us a few important deviations from the norm. Since we only needed to accommodate a heavy duty tractor truck, we could look at a streamlined or adapted wall test section and reduce the tunnel cross section significantly while maintaining very good flow characteristics. We could rely on CFD modeling to determine the wall shape. While analyzing some of our early CFD studies for various different tractors, we observed as expected, that aerodynamic tractors and traditional tractors had different local flow characteristics, with the flow separating much more from the traditional tractor. We also observed that no matter how large this flow separation was, or how aerodynamically dirty the tractor was, the flow tended to re-attach to the van trailer somewhere along its length, and the trailer base drag was pretty much the same. In other words, the back of the trailer is so far from the front of the tractor, you cannot significantly influence the trailer base drag with the tractor design. We also expected, and found, that the friction drag along the side of the trailer was relatively quite small. This allowed us another breakthrough in thinking. Since we couldn’t substantially influence the trailer drag with our tractor design, we didn’t need a complete trailer. 49
A Freightliner Cascadia under test. This production model was developed in the DTNA wind tunnel and was the basis for the Innovation Truck, that explored further aerodynamic improvements further improvements that may or may not be feasible for production or the road.
Modeling confirmed that as long as the effects of the trailer termination did not influence the upstream flow, we would not need the full length of trailer. With this realization in mind, we developed a concept where a shortened trailer is blended in at the back with the diffuser section of the tunnel. CFD showed that the tractor and front of the trailer experienced the same airflow with this concept as with a complete 53-foot van trailer. The welcome consequence was that it simplified the tunnel and reduced the test section size requirement. Moving to the power section, we quickly found that the traditional solution of designing and building a large fan was out of the question financially. Once again we went back to the basics and did a cost vs. airflow capacity analysis of many different ways of moving air, from truck engines with airplane propellers to centrifugal industrial blowers. Our most cost-favorable and straightforward solution came in the form of large axial flow fans designed for HVAC air movement in large buildings: our demands required 10 of them. 50
Since our test section ended in the shape of a horseshoe, the duct blocked by the trailer, it would be most efficient to arrange the fans in this shape, rather than change the shape back to an unblocked rectangle. We only needed a contraction cone to complete the tunnel, and it was only natural to reduce size and cost by deciding on an open return type tunnel. With a clear concept, that had several unique design elements, it was time for a reality check. We ran the concept by our aerodynamic experts in Germany and Detroit, and also our friends Jim Ross and Rabi Mehta from NASA Ames Research Center, who confirmed that the design had merit. To optimize the facility and minimize our risk, we would rely heavily on CFD, and added a talented crew of analysts to model and optimize all aspects of the tunnel, including Dan Schlesinger and Andrew McLandress from DTNA, Reinhard Blanke from Daimler in Germany, Gerald Recktenwald and Bhaskar Bhatnagar from Portland State University. They started with the test section and looked
at streamlines at various distances away from several diverse truck models. Of course the streamlines close to the body were dependant on the specific vehicle shape, but as you move away from the truck the streamlines are much more dependant on the overall size. We found the distance at which the streamlines looked similar for all the various trucks and iterated the wall shape based on these streamlines until we developed a shape that would accommodate all of the truck/ trailer models at various angles of yaw with very good correlation to free stream conditions. A 4:1 contraction cone was developed with a 5th order polynomial wall, and modeled carefully to reduce the length (and cost), without flow separation. The fans were then added to the model and a diffuser/ transition section from the test section to the fans was designed so that fan and diffuser effects would not propagate upstream into the test section. This is a very quick summary of a process that was quite involved, but we had a critical advantage with CFD analysis, that had not been available to wind tunnel designers from WIND TUNNEL INTERNATIONAL | 2009
years and decades before. This advantage allowed us to really push the envelop of conservative wind tunnel design. CFD modeling continued with the fan design, which started at with the HVAC axial fans with specially designed blades. With the open circuit design, the fans would be too loud for outside environmental noise standards. We developed an annular silencer for both the inlet and outlet sides of each fan. A challenge with multiple parallel fans is the potential for intake and exhaust pressure fluctuations between adjacent fans, leading to instability. Simply put, we again turned to 21st-century technology and in operation we rely on many sensors, controls and control logic to monitor and control the fans. The Innovation Truck in the DTNA wind tunnel. To measure aerodynamic forces on the tractor Note the elaborately faired-in rear wheels (right) we designed a flat floor balance on which to park the tractor. Since tractor design has a direct effect on the drag on so many possible the front of the trailer, the front face of the wind tunnel trailer section variants of the basic was mounted on load cells to measure its aerodynamic drag. With vehicles, we test and the drag measurement on the tractor and the “trailer” front face, we develop popular are able to optimize our tractor and its interaction with the “trailer”. customer vehicle Logically, reducing not just the tractor drag, but the sum of these two configurations, taking in to account many of the various optional features of the vehicles. sources of drag leads to optimal fuel economy. The tunnel structure was designed with standard sheet metal joist We are able to make specific recommendations for each of these structural members, with some sheet metal truss structures to support customer configurations. In addition to aerodynamic development, we conduct water soiling the larger sections. The duct was skinned with plywood, except in the test section where we used clear polycarbonate so the tests can and noise testing in the tunnel. We have devised an apparatus to introduce a calibrated amount of fluorescent rain in the tunnel, whereby be observed from outside. we are able to analyze in detail Instrumentation the rain flow patterns on mirrors is quite extensive. and glass, and integrate features This is another area to keep these surfaces clean. We where we relied hadn’t counted on noise testing on the relatively in the tunnel, as it is not quiet. inexpensive What we found however is that capabilities of the fans generate noise at a couple modern technology. of discreet very narrow band Ambient weather frequencies, which can be filtered conditions, air from the noise recordings, leaving speeds, and vehicle a very good wind noise signature. forces are measured Although the vast majority of and used to calculate work in the tunnel is with our drag coefficients own heavy trucks, weekend accurately enough shifts are added, as necessary, to to see the effects of accommodate various requests, very small model The DTNA wind tunnel under construction in Portland, Oregon geometry changes. Local flow velocities and pressures can be starting with Government studies involving heavy vehicles, measured with a multi-channel sensor system. Theatrical smoke is and including such diverse items as motorcycles, unmanned aircraft, various wheeled vehicles, and wind turbines, which are used to visualize airflow. Extensive measurements were taken as the wind tunnel was accommodated in the forward straight test section ahead of the main commissioned and compared to the CFD. We found that the CFD test section. The Freightliner wind tunnel is just one more example of the predictions were very accurate and were extremely pleased with the results that showed excellent test section flow quality, and no flow creative thinking found at DTNA, its unique design is the subject of multiple patents. It is an important tool, used extensively in the separation or instabilities anywhere in the tunnel. We began testing in earnest as soon as the tunnel was completed in design and refinement of all Freightliner and Western Star vehicles, early 2004 with the development of the new Freightliner Cascadia, and will serve for decades to come. which spent several months in the tunnel for basic shape refinement. CONTACT Since then, the tunnel has been used every day for aerodynamic Matthew Markstaller, Freightliner and other development of all DTNA products. Since there are E-mail: firstname.lastname@example.org 2009 | WIND TUNNEL INTERNATIONAL
S1MA nestled in the Maurienne Valley with the other ONERA facilities at the Modane-Avrieux Test Centre.
S1MA Fan Drive
New heart for the
The ONERA S1MA wind tunnel has been in commercial operation for the last 56 years as the largest sonic tunnel ever built. But the aging drive system and the fan blades, in particular, were becoming a maintenance nightmare which had to be addressed. A five-year program was instigated to give the S1MA a new set of fan blades and hubs (a new heart if you will). S1MA has now been setup for what we hope will be another 50+ years of operations, with reduced energy consumption and maintenance overhead. All of which translates into a better testing service for our customer. By Dr. Stephen Wolf, Business Development Manager, ONERA-GMT, France
he story of the directly by water. This was a S1M A has been clever answer to the problem of told before, and is finding 88 MegaWatts of power to far from typical. drive S1MA. This is no ordinary From its conception wind tunnel: it is a tunnel with in Germany during the early a 26.25-foot (8-m) diameter test 1940s to test the advanced section, 46 ft (14 m) in length, Messerschmitt Me 262 Schwalbe that can simulate flow velocities jet fighter, to the moving of the up to Mach 1, the speed of sound 20-percent-complete tunnel (roughly 1200 km/h or 746 mi/h). from Ötztal, Austria, to France The tunnel is closed circuit (see at the end of WWII, followed schematic opposite), and up to by the commissioning of S1MA 10 tons of air per second travels at Modane, France starting in the 1042 ft (317.6 m) that make 1950. Both sites for S1MA were up each circuit. The power to do selected primarily for one factor, this is drawn from a 2,800-foot the availability of water power. (853.4 m) head of water by two The S1MA is one of a small Pelton turbines each weighing group of wind tunnels driven 26 tons. 52
“The analyses ... confirmed that the original conception, which is about 70 year old, was daring and quite excellent”
The heart of the wind tunnel is equipped with two contrarotating fans, directly driven by the Pelton turbines. Everything associated with S1MA is massive. An upstream view of the contrarotating fans and hub assemblies typifies this (opposite), with a man adding some scale. There are 12 V1 blades, and 10 V2 blades rotating up to 230 rpm. The fan diameter is 49.2 ft (15 m), with a blade length of 12.3 ft (3.74 m) and a mean chord of 4.6 ft (1.4 m). The fan assembly weighs 54 tons. The structure of the original fan design was based on 1930s technology with a classic steel tubular spar supporting 12 ribs. The fan profiles were taken from the Göttingen 622-625 series with a straight pressure surface. In recent decades there has been an increase in tunnel operation at high speeds, which exacerbated fatigue problems. The end result was a commensurate increase in tunnel maintenance: fan blades needed to be inspected daily and, on average, 1.6 hours of insitu spot welding was required for every hour of tunnel operation. Blades had to be removed regularly for more extensive repairs, and this was a substantial commitment of time (30 percent) and effort (385 man days). Furthermore, to repair the blades outside the tunnel, 2.5 welders are employed on average each year. During the last 50 years we have built over 100 blades to keep a working set of 22 in the tunnel. We currently have on our books 50 blades – meaning that 50 have been scrapped.
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New Fan Design Since, the majority of our S1MA customers want transonic testing in the future, we were obliged to try and be more efficient in driving the tunnel at higher speed, while at the same time reducing the offdesign loads on the tunnel drive system. We chose to do this by taking advantage of improved Pelton turbine efficiency at a high 230 rpm, and improving the aerodynamic design of the fan blades with a better optimized run curve.
The aerodynamic design point of the new fan blades is positioned around the 18,700 lbs/sec (8,500 kg/sec) tunnel mass flow (roughly Mach 0.8 in the test section). The red and green curves shown on the plot, indicate how the new design is better suited to civil aircraft testing than the old design. For the aerodynamic design of the new fan blades, we turned to CFD to give us assistance. The first 3D Navier-Stokes computations were performed with “CANARI”. In addition, 2D computations
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An upstream view of the contra-rotating fans and hub assemblies, with a man adding some scale.
Schematic of the S1MA closed circuit and features.
were carried out with “COLIBRI”, a Quasi-3D code from ONERA, which has quite the same numerical features as “CANARI”. Additional computations were made with the more recent ONERA software elsA, which offers a large choice of numerical capabilities. Computations were run on the ONERA NEC SX-5 and SX-6 super-computers. A converged solution was typically achieved in 6,400 to 15,000 CPU seconds (four hours). In the end, several numerical procedures were developed to compute the flow-through S1MA fans. These calculations provided a good understanding of the aerodynamic behaviour of the fans, especially when the wind tunnel needs to operate far from the fan design point. The analyses also confirmed that the original conception, which is about 70 year old, was daring and quite excellent.
New Fan Blades A subcontractor, FläktWoods Solyvent Ventec (FSV), was selected in 2004 based on their experience with high quality centrifugal fans, and the fact they offered a well proven process to reduce the risks involved in a project of this kind. Once a fan design was selected, next came the question of how to make it. Both steel and composite materials were evaluated. The decision to go with a design utilizing high-strength steel (double the strength of the original steel) was made in March 2005. In 2006, FSV made a prototype V1 blade, to validate its fabrication techniques. This blade had a 2 in (50 mm) deflection error at the tip, while production blades have a deflection tolerance of 0.5 in (12 mm). The tolerance in cross-section shape is 0.120 in (3 mm). The steel design consists of 250 individual parts, which were welded together in various jigs. There are in fact two different blade shapes for V1 and V2 fans, but the structures are very similar. The structure is covered by a 0.120 in (3 mm) thick skin made of highstrength stainless steel, which is double the skin thickness and the strength of the original blades. This thickness is better for welding, and offers better impact resistance. The tip of each blade is hollow so the ends of the blade are “soft”. The tip clearance is not fixed due to previous tunnel damage and shape tolerances. The design is made with a theoretical tip clearance of 0.6 in (15 mm). 53
Run design curve for the new fan compared with typical test conditions and the original fan performance.
CFD analysis produced these pressure contours on the V1 and V2 fan designs.
Design Risk Reduction Since the flow through the S1MA drive system is complex, it was thought prudent to perform a small-scale test of the drive system. Consequently, FSV performed various tests using a 1/12.5 scale test rig, consisting of the complete drive system with hub supports, plus the trailing edge blowing on the two upstream V1 hub support feet. It was found (top) that the new design had a higher fan efficiency at high loss coefficients (high power operation), which is where S1MA now tends to run the majority of the time. Hence, we concluded that the off-design performance of the new fan would be better than before. Another risk reduction activity was performing a fatigue test. In this rig, the root half of a V1 fan blade was subjected to 15,000 off-centre pulls of up to 300 tons. It was estimated that this test was equivalent to 15 years of tunnel operation. The specimen root section passed this test, giving further confidence to the blade designs chosen, and reducing risk. 54
The prototype fan blade built by FSV shows its size.
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During four months, the fan blades and hubs were replaced, as seen here.
An FSV fatigue test was performed on a fan blade root section to reduce risk.
S1MA test section viewed from the contraction, with a full-span model under test.
The roughly 10% power saving due to the new fan blades is shown in this tunnel performance graph.
New fan blades being installed in 2008.
New Fan Commissioning The S1MA shut-down for a total of four months from the end of May 2008 for the fan and hub replacement. Before this back in December 2007, we performed a series of reference tests in S1MA with different tunnel operating conditions and model simulations. The hub replacements proved to be the most challenging part of the task due to the mass and size of the hubs, which were split into three parts. Nevertheless, the S1MA was ready for fan commissioning on September 26th 2008. During roughly 19 hours of testing, the S1MA test envelope was fully explored. The water consumption versus Mach number plot (above) 2009 | WIND TUNNEL INTERNATIONAL
shows a very impressive 10 percent efficiency gain (up to 9 MW). This achievement is also important in improving the blockage margin in the tunnel, whereby larger flow disturbances can now be tolerated in the test section. This opens up angle of attack ranges and model scales for certain tests. Fan blade tip movement was found to be larger than expected over certain rpm ranges, of the order Âą17 mm at 20 hz. This will require further fatigue investigation. Commissioning tests were performed using two test sections, one equipped with a fullspan model mounted on a straight sting, and the other a floor-mounted half-model.
While there was excellent repeatability for the full-span model tests, with reduced model vibration, the half-model test revealed some changes in the floor boundary layer thickness, which need to be compensated for. Overall, the more efficient operation of the tunnel has not altered the aerodynamic quality of the test section, and we are confident that customers will not notice a difference in their data. This was of course, and important objective for giving new heart to a commercially operated wind tunnel like S1MA. CONTACT Stephen Wolf E-mail: Stephen.Wolf@onera.fr 55
With regard to space, both Europe and the USA recognize that if they are to continue to be at the forefront of new developments in space then they must look towards the future. In Europe, the Future Launchers Preparatory Programme (FLPP) aims to create a Next Generation Launcher (NGL). This encompasses a number of activities with respect to the launcher system architecture and advancement in several technologies, including rocket propulsion, aerothermodynamics, reusable thermal protection systems (TPS) and hot structures, and ablative thermal protection systems for exploration missions. Similar challenges are faced in the US programmes: for example, current TPS severely limit the flight path and the mission flexibility of space transportation vehicles, requiring new innovative, multifunctional and self-healing TPS in several potential applications such as reusable launch vehicles, the military space plane and hypersonic missiles. Transition and turbulence and its impact on aerospace applications remain fundamental areas where continued research is vital if industrial aerospace design challenges are to be tackled successfully. The use of direct numerical simulation (DNS) for studying time-accurate flows in complex geometries and at high Reynolds numbers (10 5-107) which are of interest in aerospace industry is well beyond foreseeable computing power. Reynoldsâ€“Averaged Navier-Stokes (RANS) models continue to be used in engineering production codes: however, it is well known that these models encompass a number of assumptions which hinder understanding of complex flow physics especially in timedependent flows. During the past five years, research, much of it at the Fluid Mechanics Large Eddy Simulation (LES) and hybrid and Computational Science (FMaCS) Group at the Department RANS/LES methods, including the special of Aerospace Sciences of Cranfield University in the U.K., has category of the detached eddy simulation (DES) approach, have emerged as alternatives demonstrated the potential of using modern high-resolution and highand research is currently being carried out to order CFD methods in a wide range of unsteady aerospace flows. investigate the advantages and disadvantages These methods can provide much higher accuracy at moderate of different variants of these approaches. computational cost compared to conventional first- and second-order During the last 5 years, research has also methods. Professor Dimitris Drikakis explains shown that high-resolution and high-order finite volume methods can provide highomprehensive reviews undertaken by the aerospace sector have identified accuracy for a broad range of flows in both a number of challenges that must be addressed in the next 50 years. The simple and complex geometries, as well issues include noise, emissions/air quality and operational impact on climate as for a broad range of Mach and Reynolds change with regard to modern aircraft (e.g., reduced drag for lower fuel numbers, at a fraction of the computational burn per passenger mile). If these are to be successfully dealt with in future cost compared to conventional finite difference aircraft and engine designs, significant technological barriers must be overcome in order methods [references for this and others in the to produce appropriate airframe and propulsion system performance at acceptable cost text are available from the author]. Furthermore, extensive research within levels. To address the above issues radical improvements in our level of understanding and design capability in technical disciplines such as aeroacoustics, laminar flow control, FMaCS, and other research centres worldwide, shear layer manipulation and aerodynamic performance of advanced wings and blended has shown that implementation of these methods in the LES framework, the so-called wing/bodies, are required.
Methods for Aerospace
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Fig. 1: Instantaneous streamlines, slices of isovorticity contours, and pressure coefficient distribution on the suction surface of the swept wing; comparison of the clearance between the vortex core position and the wing surface as obtained by the experiment, implicit LES (3rd-order method) and a hybrid RANS/LES
implicit LES or ILES, provides very promising results in terms of DARP (Modelling and Simulation of Turbulence and Transition accuracy and efficiency, using relatively modest grid resolutions which for Aerospace, Defence Aerospace Research Partnership) wing at a can be affordable within an engineering design environment. Since the total angle of attack of 9 deg and Reynolds number of approximately ILES framework does not use any explicit turbulence model but relies 210,000, based on freestream velocity and root chord length, and a on the inherent dissipation properties of high-resolution methods, it near incompressible Mach number of 0.3. The physics of the flow is similar to that of sharp-edged delta wings, featuring: a shear-layer could also be viewed as a coarse-gird DNS approach. A few examples from the above research demonstrate the potential emanating from the leading edge; a leading-edge vortex (LEV) system that grows and becomes less stable as it progresses toward the trailing of the aforementioned methods. The first example concerns flows around swept wings, which are edge; transition around the leading edge and eventually turbulent flow. prone to transition and separation. Swept wings can be found in all Here, the ILES results have been obtained using the compressible CFD modern civil aircraft travelling at subsonic, transonic, or supersonic code, CNS3D, which encompasses a library of numerical models with speeds. Furthermore, such flows are encountered in unmanned air order of accuracy ranging from 2nd to 9th-order. The hybrid RANS/ vehicles (UAVs) and unmanned combat air vehicles (UCAVs) based on LES uses a classical second-order accurate central-difference scheme wing shapes with unconventional leading and trailing edge angles of and the dynamic Smagorinsky model. These results show that both sweep as well as complex wing-body blending. The accurate modelling ILES and RANS/LES methods exhibit a similar vortex growth as it of such flows is essential for providing designs aimed at manipulating develops towards the wing tip. The numerically predicted clearance or controlling flow over configurations, with the goal of removing is slightly higher than in the experiment but the ILES results are closer control surface dependency without penalising performance, or for low to the experiment than the hybrid RANS/LES. Another example is the flow around the ONERA RA16SC1 threeobservability assessment. The flow regimes of importance are highly skewed, or separated, boundary layers and leading edge separation element aerofoil. Comparisons between the particle image velocimetry (PIV) experiment and three different CFD strategies, the unsteady resulting in shear-layer roll-up. Figure 1 shows results time-accurate simulations for the MSTTAR RANS (URANS), DES and ILES, have been obtained. The experiment
Figure 2. Contours of velocity and averaged streamlines in the flap region: Comparison between different CFD strategies, including URANS, DES and ILES, and the experiment
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(Fig. 2) shows that the flow separates near the trailing edge of the flap. The DES and URANS approaches predict attached flow, whereas flow separation is predicted by the ILES approach using a 3rd-order WENO scheme in conjunction with low-Mach correction techniques.
Figure 4: An example from the application of FMaCS groupâ€™s CFD methods to helicopter flows. The results show vorticity contours around a helicopter as obtained by ILES and DES methods. The same iso-vorticity contour values are used for both methods
Implicit LES (5th-order)
The use of high-resolution and highorder methods in combination with highperformance computing (HPC) has recently enabled their implementation in complex air vehicle configurations (e.g. UAVs), including embedded flow control devices and thrust vectoring systems. Figure 3 (opposite page and main image) shows a snapshot of the flow around a UAV. Recent CFD developments in the FMaCS Group have enabled very high-order of accuracy, e.g., 9th-order, on unstructured hexahedral/tetrahedral grids, as well as high parallel efficiencies up to 97% on 128 CPUs using proper cache memory utilisation. Figure 4 shows ILES and DES results using 5th-order methods for helicopter flows (computations performed in the framework of the GOAHEAD project). The iso-vorticity contours demonstrate that the ILES solution
Detached Eddy Simulation
Figure 5: Comparison of 2nd-order (MUSCL) and 5th-order (WENO) methods for heat transfer predictions of real-gas hypersonic flow around a double cone geometry; the geometry and Mach iso-lines are also shown
Figure 6: Flow modelling of gas turbine combustor model: (a) schematic of the model; (b) instantaneous snapshot of fuel volume fraction in y/D = 0 plane; (c) mean axial velocity profile comparisons between 5th-order ILES, classical LES and experiment
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The figure shows comparisons for the mean exhibits finer-scale axial velocity between experimental data, flow features on the 5th-order ILES and classical LES (based on same grid. Smagorinsky subgrid scale model and a 2ndThe potential of order central scheme). these modern CFD The examples presented here show that methods has been advanced CFD methods in combination with further explored HPC allow a tremendous degree of simulation in hypersonic and capability to be accessed. In particular, combustion flows. Large Eddy Simulation methods based on Figure 5 shows high-resolution and high-order methods results from the provide a promising simulation strategy for implementation of unsteady aerospace flows. Current research 2nd-order MUSCL includes quantification of numerical and 5th-order WENO uncertainty, issues of initial and boundary methods in real-gas conditions, as well as the use of CFD for hypersonic flows designing wind tunnel experiments. The around a doublecombined effort of carefully-designed cone at Mach number experiments and CFD will allow us to of 12.7. The results elucidate fundamental questions about the demonstrate that 5thflow physics, as well as to obtain data for order WENO methods An example from the application of the FMaCS Group’s CFD methods to UAVs. Instantaneous streamlines as validating advanced CFD methods in complex improve the heat obtained from parallel computations using high-order aerospace applications. transfer predictions unstructured grid methods in certain flow regions. Investigation of the accuracy of different LES methods has also CONTACT been performed for turbulent jet flows in gas turbine combustors. Professor Dimitris Drikakis Fluid Mechanics and Computational Science (FMaCS) The jet injector geometry shown in Figure 6 was also investigated Department of Aerospace Sciences experimentally. The fuel is injected in the axial direction through Cranfield University the round nozzle with the oxidiser being supplied in the axial E-mail: email@example.com direction from an annulus inlet and constant air flow as co-flow. www.cranfield.ac.uk/soe/profiles/d_drikakis.jsp
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www.pco.de in America: www.cookecorp.com 2009 | WIND TUNNEL INTERNATIONAL
Safer Skies: Pilot Training for Icing Effects Wind-tunnel testing of aircraft ice-accumulation effects and the accurate modeling of these effects in flight simulation can better prepare pilots for in-flight icing conditions. By Brian Wachter, Director, Marketing & Business Development, Bihrle Applied Research Inc with NASA Glenn Research Center
he February 12, 2009 crash of Continental Connection Flight 3407 five miles short of the Buffalo Niagara International Airport in New York USA, which killed 50 people, highlights the importance of pilot training for flight in conditions, such as icing, that can lead to aircraft upset and loss of control. Unfortunately, even the most sophisticated flight simulators in use today for pilot training include only simple iceeffects models that do little to prepare pilots for the adverse flying qualities exhibited by aircraft in severe icing conditions. Recognition of the need for improvements in pilot training is not new. In 1997, NASA formed the Aviation Safety Program (AvSP) in response to a White House Initiative to reduce aviation accidents. The program was tasked to reduce aviation accident rates by
WIND TUNNEL INTERNATIONAL | 2009
Ice Contamination Effects Flight Training Device in action (above and below, opposite)
2009 WIND TUNNEL INTERNATIONAL ELD WTI| HP 0909.indd 1
90 percent by 2017. Since 13 percent of all weather-related accidents were found to be due to airframe icing, NASA Glenn Research Center sought to develop a sophisticated flight simulator specifically designed to demonstrate the effects of in-flight icing and train pilots to recognize and respond to the adverse flying qualities associated with ice accumulation on the aircraft. This simulator became known as the Ice Contamination Effects Flight Training Device or ICEFTD. The initial airplane chosen for the activity was the DeHavilland DHCâ€“6 Twin Otter since NASA had extensive operational experience in icing conditions with this airplane and flight records that would be useful in the modeling and validation efforts were available. The Twin Otter also has a known sensitivity to ice contaminated tail-plane stall. NASA Glenn engineers understood that in order for the ICEFTD to be effective, it would need to model ice accumulation and the resulting impact on aircraft flying qualities to a much higher degree of accuracy and realism than was typically found in current training devices. Icing effects in even the most sophisticated present-day flight simulators are simple models that do little more than increase drag and increase weight to simulate in-flight icing.
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BIHRLE Ice shape mounted to the leading edge of the DeHavilland DHC-6 aircraft in preparation for ice accumulation effects flight testing.
Tail-plane icing can cause significant yoke forces approaching tail stall with the Twin Otterâ€™s reversible control system ... over 100 lbs pull force!
Representative ice shape used on wind tunnel model
In order to allow pilots to recognize important visual and handling quality cues associated with an icing event, these simulation models would benefit from physics-based models that realistically model the aerodynamic effects of airframe icing. Incorporating such high-fidelity models of icing effects into flight training simulators used for initial and recurrent training would allow pilots to experience representative icing-induced aircraft handling characteristics, especially in failure case training scenarios. A primary goal of the ICEFTD program was to develop a methodology that could be applied to any flight simulator to extend its capabilities to include accurate icing effects training. This methodology involved the acquisition of aerodynamic data for icing conditions and the mechanization of this data into a mathematical model for use in flight simulators. In order to prove the viability of this methodology, it was necessary to demonstrate that subscale wind tunnel testing of iced airplane models could yield aerodynamic data of sufficient fidelity that the icing effects could be accurately replicated. Consequently, one of the first steps was to conduct a series of wind tunnel tests to assess scaling of the ice effects for full-scale, 42 percent- and 7 percent-scale 62
Twin Otter tail sections using geometricallyscaled ice shapes. Tests were also conducted to identify â€œequivalentâ€? ice shapes that were less complex, but which would produce the correct aerodynamic effects at typical wind tunnel test scales. When considering the aerodynamic effects of ice on an airplane configuration, the effects of drag on the airfoils are not isolated, but couple into the pitching moment of the airplane. The lift degradation on the horizontal tail also couples into the airplane pitching moment not only in a static sense, but also in a dynamic sense by changing pitch damping as a function of angle of attack. Lift degradation on the wing can affect longitudinal stability and roll damping. Adding the consequence of reduced control surface effectiveness can
lead to an aircraft with substantially degraded stability and control and handling qualities. As a result, forced oscillation and rotary balance tests were conducted to gather the dynamic data using the Bihrle Applied Research Inc Large Amplitude Multi-Purpose (LAMP) wind tunnel located in Neuburg, Germany. These data, in addition to static data, were collected in order to comprehensively develop and model the full range of iced aircraft flight dynamics.
Simulation Math Model The next step required the development of comprehensive nonlinear flight simulation models that utilized the aerodynamic databases derived from wind-tunnel test results. Simulation models were developed
NASA Twin Otter Flight Test Aircraft
WIND TUNNEL INTERNATIONAL | 2009
for the No-Ice (clean) and two ice protection system (IPS) failure iceshape configurations. The models were hosted in BAR’s Commercial Off the Shelf (COTS) DSix® simulation environment, which provides numerous analytical tools to provide for the rapid implementation and validation of the mathematical models. In order to validate the model, a series of flights of NASA’s Twin Otter Icing Research airplane were made with the same ice shapes and conditions that were simulated in the wind tunnel test. The model development featured a rigorous validation of the basic Twin Otter flight model, culminating in piloted evaluation of all model configurations using NASA test pilots. One key objective of the research effort was to enable real-time, “pilot-in-the-loop” simulation to demonstrate icing effects on flight dynamics to pilots and engineers. DSix provided the simulation environment to accomplish this
because it permits the dynamic linking of other object modules that can control everything from the simulation integration scheme to external graphics and network communications with no requirement to edit the flight model code. Following the successful math model development and validation effort, the actual flighttraining device was manufactured. Since tail-plane icing can cause significant yoke forces near tail stall with the Twin Otter’s reversible control system (over 100 lbs pull force!), a high-fidelity longitudinal force loader system was a fundamental requirement for the ICEFTD. The Input/Output Device (IOD) interface provided by the DSix simulation software enabled the simple and direct integration of a high capacity Moog/FCS stick loader. In addition to the control loading system, the ICEFTD incorporated a full set of representative pilot control input devices, basic flight instrument and ILS displays
Scale model of the DeHavilland DHC-6 aircraft mounted in the LAMP wind tunnel in preparation for dynamic testing (above and below)
Angle of Attack (deg) Effect of Ice on Twin Otter Normal Force (flaps=20 deg)
Alpha Effect of Ice Protection System (IPS) Failure on Twin Otter Pitching Moment
Schematic of development process
suitable for landing tasks, triple screen outthe-window graphics, and an interactive instructor station. It was also designed to be portable so that it can be easily taken on the road to off-site training venues, with wheels for transport and even sized to fit through an office doorway. A training curriculum was developed for the ICEFTD in order to familiarize the training pilot with the basic flight characteristics
of the Twin Otter in no-ice and fully-iced configurations. This allows the pilot to compare and contrast the changes in stall and handling characteristics. Additionally, a scenario-based lesson was used to demonstrate icing effects during the approach to landing segment of a flight. The ICEFTD has been used in pilot workshops to demonstrate the cues to recognize iced airplane handling qualities, and the appropriate recovery techniques should a
handling anomaly occur. The ICEFTD was successfully demonstrated to over a hundred pilots and flight test engineers through multiple venues. Training sessions familiarized pilots with the aircraft simulation, illustrated differences in wing and tail stall character due to ice shapes, identified cues and variables that reduce or exacerbate the problems, and, lastly, placed the pilots in an operational scenario with the iced aircraft to demonstrate the potential extent of the problem icing can pose. All of the pilots who participated in the demonstrations were complimentary of the ICEFTD and found the training to be applicable to their occupations. The ICEFTD successfully demonstrated that icing effects can be modeled accurately in flight training devices to show how these effects significantly alter flying qualities. Clearly, simply increasing drag and increasing weight in pilot training simulators does not sufficiently model the change in stall characteristics that pilots would experience in real-world operations. This effort demonstrated that highly accurate simulation models can be developed when employing the wind tunnel test and simulation development methodologies described herein. Applying these same methodologies to other aircraft will result in high-fidelity simulation models that can be incorporated into full flight simulators to provide flight-representative icing effects training capabilities that will no doubt make for safer skies. CONTACT Brian Wachter E-mail: firstname.lastname@example.org
WIND TUNNEL INTERNATIONAL | 2009
High performance industrial fans Touch screen control panel
Professional training of a 4-way FS team
Sustainable, quiet wind for
work and play
Just after the Millennium, two independent Europeans got together to create what has become one of the most exciting businesses in the wind tunnel industry
n 2003 André Kempenaars
Return Air System for Roosendaal wind tunnel
and Gerard Malempré, met each other and started to share their knowledge, experiences and, most of all, their future business plans. André had travelled with his family all over the world in 2000 to gain an overall experience of the vertical wind tunnel business. After being a CEO of an independent software testing consultancy for 18 years, he was seeking for new adventures. André was also an addicted skydiver….Gerard had been invited by AEROKART in 2001 to create solutions for the first vertical wind tunnel under construction in Paris, France. Gerard was already a specialized fan engineer with more than 30 years’ experience.
They found such strong agreement that they started to work together. In 2006, André opened the first full commercial indoor skydive centre in the Netherlands, with Gerard at his side as the main engineer of the wind tunnel element. It turned out not only to be the fastest vertical wind tunnel worldwide, but also the most silent one. 66
are very keen in having the best facilities for their troops to train paratroopers – not only for military purposes but also for competitive sport events. Military troops use our products to become the best in the world With the knowledge and experience of developing and building two full equipped return air vertical wind tunnel centers in Paris France and Roosendaal, in the Netherlands, AIR2TUNNEL EUROPE still wants to improve in areas that may, to the eye, appear minor but are major from a technical point of view.
Airflow calculation with a CFD application
Current developments After having realized two separate projects André Kempenaars and Gerard Malempré decided to join knowledge in sales and engineering and AIR2TUNNEL EUROPE became a fact. AIR2TUNNEL EUROPE is an organization that depends on two markets: recreational and professional/military. The recreational market, where people can experience the feeling of a freefall without jumping out of an airplane is very big but also very sensitive to the current economical situation. In the professional/military market, armed forces
The most important feature AIR2TUNNEL EUROPE has worked on since it developed the two skydive centers is the usage of energy. AIR2TUNNEL EUROPE already uses high performance electrical motors, high end industrial fans and top quality frequency drives, which can be operated via a web interface. The advantage of using these components is standardization. All components are available at multiple sales points worldwide. To control the energy consumption many simple solutions are used to improve efficiency. Higher-than-normal energy consumption is a fact in operating any type of wind tunnel but AIR2TUNNEL EUROPE WIND TUNNEL INTERNATIONAL | 2009
Armed forces are very keen in having the best facilities for their troops to train paratroopers — not only for military purposes but also for competitive sport events airflow, AIR2TUNNEL EUROPE is using a computational fluid dynamics (CFD) application, in which we can easily detect any instabilities in the proposed airflow. With this application we can easily calculate the pressure drops that occur for different objects in the wind tunnel. So we can calculate, for example, the exact pressure that’s necessary to have a professional 4-FS (four-person formation) skydiving team in the flight chamber or a fully equipped military paratrooper.
360 degrees visibility!
has built in a feature that creates the possibilities to generate energy in operating all our model wind tunnels. The energy that is generated can be reused for other operational items in the skydive center, but also for powering the electrical motors. The generated energy can also be delivered back to the energy companies. Average savings can add up to 35-40% of annual energy consumption.
Maintenance AIR2TUNNEL EUROPE is also experienced in maintaining older types of vertical wind tunnels, whether single- or multi-propeller versions, electrical or diesel-powered. We can offer a suitable solution for almost every model.
Turnkey Noise pollution
AIR2TUNNEL EUROPE is combining all above features in a Vertical wind tunnels are not new. They have been around for many complete package. We can offer from just the design of a fan to a years. However, most versions have been open-type tunnels powered tailor-made complete turnkey project for the customer. To complement by diesel engines, that were extremely loud for the surrounding our current active operations in Europe, Africa, China and the Middle East, we are areas. More sophisticated models setting up an agency have been introduced but noise in Lithuania for pollution has remained a problem. Eastern Europe and In both its Paris and Roosendaal Russia. With this locations, AIR2TUNNEL EUROPE extra sales point, has brought down the external we can serve more sound level to less than 45 dB. future clients with our Due to the wind tunnel’s interior next-generation wind construction, the external sound tunnels. level is so low that one location The next time even has an operating open-air you fly in a vertical restaurant immediately next door. wind tunnel, you’ll The trees outside make more experience an noise whispering in the breeze absolute adrenaline than the wind tunnel running at rush, with taking in full speed! consideration, that if it’s an AIR2TUNNEL Stable airflow EUROPE model, Another very important issue you’ve actually flew in vertical wind tunnels, where for a sustainable body flying is the core business, is Family fun! environment! generating a stable airflow. Don’t forget to smile when you’re flying!!! The engineering department of AIR2TUNNEL is located in Paris, where the calculations are made to create the most stable airflow in the flight chambers. For body flying you need the same amount of air CONTACT with the same speed at everywhere at the same height in the flight Andre Kempenaars Air2Tunnel Europe chamber. For these studies and calculations to achieve the most stable E-mail: email@example.com 2009 | WIND TUNNEL INTERNATIONAL
Just like real racing Simulating the dynamic behavior of a ground vehicle
Most wind tunnel measurements with ground vehicles are performed with models that are kept stationary with respect to ride height and pitch. But tests carried out with a race car model confirm that transient aerodynamic effects resulting from height and pitch must not be ignored if best performance is needed. With a novel model manipulator, it is possible to simulate the dynamic behavior of the vehicle over the track and at the same time measure its aerodynamic performance. By Claus Zimmerman, Measurement Technology Team Leader, RUAG Aerospace for HBM
WIND TUNNEL INTERNATIONAL | 2009
Le Mans car model (30 percent) in the automotive wind tunnel. At no time during this test do the wheels touch the model; they are held in the correct place by special wheel arms at the side
he aerodynamic performance of new vehicles is often optimized in wind tunnels. Reduced-scale models are positioned in the wind on an aerodynamically shaped mount. Sensors built into the model provide data on aerodynamic forces and moments, as well as pressure values on the surface of the model.
Aerodynamicists use both measured and numerically derived characteristics to decide on necessary design changes. In wind tunnel testing, normally only mean values for aerodynamic characteristics such as lift/downforce and drag are determined, so that the estimate of test object properties is as reproducible as possible. But the latest investigations at the Center Aerodynamics of RUAG Aerospace in Emmen, Switzerland show that the use of aerodynamic mean values is not always correct. Fluctuations caused by flow separation, natural air turbulence or the usually unavoidable natural motion of the test object relative to the wind, cause the instantaneous value to vary from the mean by unexpectedly large amounts. These instantaneous values are very useful for the development of highly optimized racing cars as well as more conservatively designed production cars, for keeping the distribution of force on the front and rear wheels in the safe range at every moment and to achieve good and reliable handling characteristics. To realistically simulate vehicle movements in the wind tunnel, vertical movements of several millimeters in amplitude are induced to the wheel axles, at frequencies up to more than 20 Hz. A hydraulic A selection of multi-component balances, as used in wind tunnel testing. The smallest balance weighs 0.25 kg, the largest 112 kg
2009 | WIND TUNNEL INTERNATIONAL
“shaker” with a control unit has been developed to produce such motions on the wind tunnel model. In the model, the shaker is located beneath the weighing sensor – the balance – that in turn is fixed at the vertically aligned model support protruding through the roof of the model. Separation of aerodynamic forces from the often considerably greater inertial forces caused by the above described movements poses a particular challenge in this measurement task, as the balance itself can only account for the sum of these forces and moments. To accomplish this partitioning with sufficient precision, the recording of about 100 measurement channels must be perfectly synchronized and analyzed. High-quality measurement data at sampling rates from 400 Hz upwards are the basis for this task.
Special six-component balance The six aerodynamic forces and moments (drag, side force, lift/ downforce, rolling moment, pitching moment and yawing moment) that act on the test object during the wind tunnel test are determined with a special six-component balance integrated into the shaker. Providing excellent quality of signal conditioning and amplifier, the balance meets stringent demands for accuracy at minimal dimensions and extreme stiffness. Strain gauges are applied as full Wheatstone bridges on the balance measuring beams. In order to cope with temperature variations, the wiring is thermally compensated. The measuring beams under the action of the load only minimally deform in the elastic range and produce output signals in the strain gauges proportional to the applied load. The correlation between these electrical signals and the actual load is determined by a balance calibration procedure carried out subsequent to fabrication. This procedure takes place with calibrated mass weights and a Data acquisition system with calibration device connected to the HBM MGCplus technology: Front (on the left) and back with connection balance offering various pivot options. boards (on the right) 69
By attaching the weights to these pivot points on the model side of the balance, pure forces or a combination of a force and up to two moments can be applied on the balance. The calibration matrix, defining the relationship between load values and electrical strain gage values, is derived by a regression algorithm that takes into account all the well-defined load cases which that were applied during the calibration process. The inverted matrix, defining the relationship between electrical values and load values, allows the calculation of the applied forces and moments from the electrical measurement signals as is needed during measurement. For some years, RUAG Aerospace has relied on HBM’s MGCplus
technology for data acquisition in its wind tunnels. By choosing different amplifier types and combining the amplifiers with the proper connection boards, it is possible to meet the demands for accuracy (divided into accuracy classes) as well as for a wide variety of possible sensor types. For each wind tunnel at the Center Aerodynamics, the hardware components have been integrated into a flexible, easy-touse complete system in a cabinet with various monitoring devices. For practical reasons, it was decided to use standard modular The “shaker” model movement unit built into the vehicle model, enclosure systems on rollers with with model mounting five MGCplus housings, with the amplifier displays and control buttons at the front and standard connection boards with sockets for the power, measurement signal and data lines at the back. Drivers for communication between the hardware and the company’s own master computer and data analysis software also had to be created and adapted to the specific measurement tasks. Finally, a special calibration system/procedure was developed for the measurement system, for flexibility, and, most importantly, for quick on-site use within the expensive wind tunnel test environment that enabled the tracing back of all the different system components to national standards.
Specialized in developing, designing, engineering and building vertical wind tunnels for recreational and professional usage.
P.O. Box 1560 4700 BN Roosendaal The Netherlands .+31653-99.89.89 +31847-36.53.79 firstname.lastname@example.org
9 Alleé de la Madeleine 77123 Noisy Sur Ecole France +33164-24.06.33 +33164-27.70.41 email@example.com
Motion greatly influences aerodynamics In first wind tunnel test campaigns with the moving model, motion trajectories were initiated at frequencies up to 10 Hz, for 20 second periods, in order to search for transient aerodynamic phenomena. The movements took the front and rear axles of the vehicle model up to 4 mm out of the standard position, the front and rear axle being either fully in phase, 180° out of phase or the rear axle being kept still. A sampling rate of 400 Hz was specified for these tests by weighing up the timing resolution and the amount of data this would produce. Once data is available from a wind tunnel test with time-resolved measurement, there are many possible ways to evaluate it. In the initial phase, non-linear filtering is applied, in order to reduce the noise component of the individual measurements. Then the inertial forces are calculated and subtracted from the total forces, for which signals from the acceleration transducers at selected model positions are consulted. With the calculated result a number of relevant stability problems caused by the interplay of aerodynamics with the chassis dynamics can be analyzed in detail and used to characterize the drivability or even the safety of the vehicle configuration at hand. This method of measurement allows the optimization of the vehicle not just to the lab-like conditions in the wind tunnel but also, by simulating realistic vehicle movements, to real situations that occur on the track. height above ground
negative lift of the moving body
for light-, medium-, heavy-duty vehicles, motorcycles, ATVs, ...
negative lift of the fixed body 1.2
12 1.05 10 1 8 0.95 6
downforce coefficient (scaled) [-]
height above ground [mm]
True Test Tracks
4WD Chassis Dyno (4-motor-principle)
The accompanying figure shows the time varying downforce coefficient (negative lift) of a simplified model of a Le Mans® racing car moved at 10 Hz compared to static measurements. The green curve describes the movement when, in this case, the front and rear axles move up and down in phase at an amplitude of 4 mm. As is usual for race cars, there was very little ground clearance for this test, so that the nose of the model approached to within about 2 mm of the ground. The red curve describes the downforce measurements with a fixed model. To derive this curve, the model was taken to every one of the given positions, was fixed in position and the average downforce level was established; in the configuration shown, there proves to be only a slight dependency between the downforce coefficient and the height above ground. The situation is completely different when measurement and analysis are time-resolved and relate to the moving model (blue curve). The enormous differences from the mean value indicate that the movement causes vast fluctuations in aerodynamic force and moment, which under certain circumstances can greatly influence the stability of the vehicle. CONTACT Chantelle Thompson, HBM E-mail: firstname.lastname@example.org 2009 | WIND TUNNEL INTERNATIONAL
MAHA-AIP (Automotive Industry Products) designs individual vehicle test stand solutions for most well-known vehicle manufacturers, their sub-suppliers and certification labs. Test drives can be simulated with reproducable test results indoors to improve product quality and optimize costs.
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Flat Road Dynos and Chassis Dynos for Wind Tunnel Applications Chassis Dynos for e.g.: Emission-, NVH-, EMC-, Climatic-, and Mileage Accumulation Tests Hydraulic Road Simulation Test Stands (4-Poster, etc.) Emission Measuring Systems Automation
Reliable test results under any condition Contact us with your specific requirements, and we will present you with a customized proposal!
Flat Road Dyno with steel belt
MAHA-AIP GmbH & Co. KG Automotive Industry Products Hoyen 20 · D-87490 Haldenwang / Germany Tel.: +49 (0)8374-585-0 · Fax: +49 (0)8374-585-551 eMail: email@example.com · www.maha-aip.com
Acoustic vector sensors in Aeroacoustics
Regular particle velocity sensor
The Netherlands-based company Microflown Technologies offers aero acousticians novel experimental methods for wind tunnel testing. All applications are based upon the Microflown, the worldâ€™s first and only dedicated acoustic particle velocity in-air sensor. Microflown Technologies is actively involved in the EU FP 7 framework program for aeronautics, contributing to several research lines on both jet noise and airframe noise reduction, explains Hans-Elias de Bree, director of R&D.
ny sound field is fully described by both its scalar value sound pressure and its vector value acoustic particle velocity. If sound pressure were the acoustic equivalent of voltage, acoustic particle velocity would be the acoustic equivalent of amperes.
Remarkably enough, acoustic particle velocity was never a directly measurable quantity in acoustics. Sound pressure gradients were used to compute acoustic particle velocity. With the availability of a dedicated acoustic particle velocity sensor in air, new possibilities arise for both acoustic far-field and acoustic near-field sound-source localization techniques. It also becomes possible to measure in-situ the acoustic absorption on all sorts of aerospace materials. 72
Sensor working principle In essence, the Microflown is an extremely sensitive thermal massflow sensor as it is enabled by MEMS technology. The working principle is based upon the measurement of the temperature difference between two closely spaced heated platinum wires. Over its entire bandwidth, the Microflown sensor is linear, showing some high frequency decay. A flat output signal can be obtained by software adjustments of the amplitude and phase.
Hot-wire comparison There are important differences as compared to the well-known single hot-wire systems. The two-wire system makes the sensor directional as the temperature difference has the same sign as the sign of the velocity. WIND TUNNEL INTERNATIONAL | 2009
A miniature version of a 3D vector probe, shown with a match head for sizing
Furthermore, the Microflown sensor is linear, whereas a single hotwire cools down with the square root of the velocity. Also, the performance of the Microflown sensor only depends upon the temperature difference whereas a hot wire is sensitive to the ambient temperature itself. Fourth, but not least, the sensitivity of the Microflown is much higher than a single wire solution (detection range goes down to 10nm/s).
Simultaneous aerodynamic and aero acoustic testing Sound-intensity-based measurements based upon PU or USP probes can be carried out in non-anechoic conditions. This sheer fact enables operators of non-anechoic wind tunnels, the far larger part of the total installed facility base, to combine aerodynamic and aero acoustic testing in closed-section wind tunnels. Apart from the obvious efficiency gains, better consistency in datasets is also an important merit.
Products One or three Microflown particle velocity sensors can be combined with a sound pressure transducer, resulting in a range of one (=PU) and three dimensional sound probes (=USP) that can be used under a variety of wind tunnel operating conditions. 2009 | WIND TUNNEL INTERNATIONAL
Wind-tunnel-relevant developments Targeting the wind-tunnel-testing markets, several developments took place during recent years in the Netherlands at various national institutes. 73
PU measurement in small anechoic windtunnel
Microflown sound probes and sound chips might offer a third way (to carry out non-invasive testing), allowing multi point measurements in a broad frequency range For lower intrusiveness, the assembled Microflown three dimensional USP probe was reduced to one single flat monolithic chip, still measuring the 3D particle velocity vector and the sound pressure. In the flow, wind tunnel measurements were proven to be possible up to landing speed conditions of around 70 m/s. Just as a sound-pressure microphone, the Microflown sensor is sensitive to wind. Placing both types of transducers in a low intrusive wind cap (nose cone) allows sound intensity data to be obtained. From a signal processing point of view, it is beneficial that the wind has an uncorrelated influence on both signals (i.e. particle velocity and sound pressure) obtained. The frequency range of the Microflown sensor was increased up to 120 kHz, adversely affecting its signal to noise ratio obviously at higher frequencies. For cryogenic testing, the Microflown sensor was successfully tested as well. 74
Limitations of beam forming techniques Acoustic far-field sound-source localization techniques have always been based upon an array of sound pressure transducers that is large, both in channel count and physical dimensions. Measuring time delays, they only use, in effect, phase information of the sound field. Intrinsically, there are limitations in the lower frequency range, and beam forming arrays can not pinpoint the 3D location of a noise source. This is of relevance to airframe noise, where the noise sources are usually located around the object, not at its surface itself. Acoustic vector sensor-based far-field soundsource localization techniques As an alternative to beam forming, the concept of vector sensors in air is known in several frequency domains like radar or cellular phones. In the audio range, it is also known in underwater acoustics, using accelerometers
to approximate the particle velocity. Vector sensors use both phase and amplitude information. This richness in information can be used in a range of signal-processing techniques, for instance using cross-correlation techniques in MUSIC and PARAFAC algorithms. Simulations supported by experiments showed that a number of N acoustic-vector sensors can locate and track in a 3D space up to 4*N-2 narrow banded sound sources simultaneously. For broad-banded sound sources, first simulations indicate 8*N-2 sound sources to be separated. Only a very compact array in terms of physical size and channel count would be necessary compared to large amount of probes that are required with traditional beam forming arrays. It would reduce installation time and overall dimensions of the array.
Near-field sound-source localization techniques From an acousticianâ€™s point of view, acoustic near-field measurements are the preferable option to investigate soundsource mechanisms, yielding relevant phase and amplitude information. Obviously, aerodynamicists prefer non-intrusive WIND TUNNEL INTERNATIONAL | 2009
techniques, resulting in trade-offs to be made depending upon circumstances. Microflownbased techniques offer a new alternative. Sometimes optical or far field beamforming techniques don’t have a line of sight to the object, leaving no other option than lowintrusive acoustic near-field measurements. For novel extremely small active-control techniques, a higher level of spatial resolution is required than possible with far-field beam forming. Details in landing gear can not be measured with accelerometers, as they don’t measure flow induced noise. PU probes can be used for acoustic near field measurements here.
In-situ acoustic-absorption measurement of aerospace materials
A velocity sensor with a micro machined windshield, combined with a miniature sound pressure microphone, is mounted in a nose cone
Several types of so-called porous airfoils are being developed to reduce noise levels, requiring a trade-off between aerodynamic and aeroacoustic properties such as flow resistivity and acoustic absorption. Microflown probes measure both sound pressure and acoustic particle velocity right at the surface of the material, allowing the acoustic absorption to be derived according to
the formulas and on the very spot as installed. As there was hardly an alternative, Kundts tube type of measurements were mostly used to measure acoustic absorption. But this approach is destructive and can only measure absorption under a normal angle of sound wave incidence, which is rarely the case in practice. Furthermore, is it not possible to measure under flow conditions. Results of PU in-situ-based testing on microperforated jet-engine liners subjected to a flow study carried out in 2008 clearly demonstrated the need for in-situ in-flow measurements as an alternative to other existing methods widely applied.
Future developments Further clean-room sensor developments are underway to achieve: • even lower intrusiveness of the 3 D sound chip • wind speeds up to 150 m/s (Mach 0.5) • increases in S/N ratios up to 100 kHz CONTACT Hans-Elias de Bree, Microflown Technologies E-mail: firstname.lastname@example.org
icroflownTechnologies Charting sound fields
Acoustic Vector Sensors for windtunnel testing
Far field sound source localization Near field sound source localization In situ absorption Plots in 3D space No line of sight required Also on small objects Microflown Technologies, PO Box 300, 6900 AH Zevenaar, The Netherlands W: www.microflown.com E: email@example.com T: +31 316 581490 F: +31 316 581491 2009 | WIND TUNNEL INTERNATIONAL
The Schlieren Imaging Method and Related Components
n the study of ballistics, Schlieren imaging discloses valuable normal sensitivity system consists of a main mirror, two knife edges, information concerning shock waves accompanying projectiles focusing lens, light source and camera, while a high sensitivity system and missiles. The combustion engineer uses Schlieren imaging includes two mirrors, two knife edges, focusing lens, light source and in studying how fuel burns, and investigation of heat transfer camera. There are many variations of these arrangements. The beginning of high speed photography & Schlieren imaging is aided by the ability of Schlieren imaging to show the paths over a hot surface. In general, the Schlieren imaging technique might be considered to be William Henry Fox Talbot’s experiment in can be used to advantage whenever it is desirable to visualize the 1851. He attached a page of the London Times newspaper to a wheel, flow of gases. Movements of the surface of a liquid and convection which was rotated in front of his wet plate camera in a darkened currents within liquids during heating and cooling can also be room. As the wheel rotated, Talbot exposed a few square inches of the newspaper page for about 1/2000th of a recorded using variations of this second, using spark illumination from Leyden technique. jars. This experiment resulted in a readable Because of its optical approach, image. Wet plates, called “amphyitypes”, Schlieren imaging does not were used. These glass plates were coated interfere with the subject being with a mixture of albumen, silver nitrate, observed as the normal motion of and water (approximate ASA less than 4). gases is not impeded, unlike when Considering the extremely low sensitivity of pilot tubes, yaw tubes or other these plates and the limitations of the lenses intrusive methods are inserted Color image of explosion under water that were available (probably about f/32), this into the gas stream to detect flow (Hunting Engineering, UK) photograph was a remarkable achievement. direction. This is particularly Some further work important at high gas velocities, where shock waves set up by probes Black/white image of 12 bore shot exiting barrel was done in 1856 by in the stream will seriously distort the data. (Pulse Photonics, UK) Foucault and in 1864 The sensitivity of Schlieren imaging can be made surprisingly wideby Toepler, followed ranging. It can easily detect temperature differences as small as 5ºC in an by Wood and others, air stream making it adequate to disclose the currents of heated air rising which resulted in from a person’s hand. Conversely, the sensitivity can be reduced to the the development point where the exhaust of a liquid fuelled rocket with a temperature of Schlieren of more than 2690ºC can be recorded to show the presence of shock photography for waves and other flow phenomena. A Schlieren imaging system can studying wave fronts be modified to give a and other effects very good example of of variations in shadow photographic transparent media. imaging. At Wo o l w i c h Compared to other Arsenal near London, intrusive and high experiments were end imaging systems, conducted in 1861 the Schlieren imaging Black/white shadowgraph image of using shadowgraphs system is relatively shaped charge speed 1500metres per second (Hunting Engineering, UK) to study projectiles inexpensive. A 76
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such as human and sports movement investigations and some slower ballistics studies (but not ideal for Schlieren imaging applications due to their relatively long arc plasma path); and open spark systems well suited for Schlieren imaging because of their very short pulse durations. Open Spark light sources are used in applications where the subject is very fast or ultra fast, with durations typically from 1 microsecond down to 100 nanoseconds. These open spark systems are capable of capturing Schlieren images of missiles Schlieren imaging has become an and ballistics with speeds of 3000 m/sec and more. indispensable tool for investigating the flow The earliest recorded example of an open spark of gases. This is particularly true in the source would be Fox Talbot’s experiment in 1851 mentioned earlier. aeronautical, automotive, liquid and combustion Although more than a century and a half has passed engineering fields, where knowledge of the air since Fox Talbot’s experiment, the basic technology and liquid flow patterns over surfaces is increasingly and principles are still used to this day. The modern important due to environmental and economic concerns. version of the open spark light source is the Palflash Model 501, originally called the Argon Spark when By Steve Daicos, President, The Cooke Corporation it was first manufactured in 1977 for use in the Rolls-Royce aero engine plant in Derby, UK. To date there has been more than 600 built. The Palflash in flight. The projectile was launched between 501 has durations from 1 microsecond down to 100 a camera and a 100 microsecond duration nanosecond and is used in conjunction with argon light source. This technique was perfected gas to improve its spatial stability. It has up to many years later by Ernst Mach in Austria and four spark channels to record multiple images of Sir Charles Boys in England. The suggestion high-speed events both for Schlieren and normal was made by Alfred A. Pollock in 1867 that high-speed images. Although the Palflash 501 was it would be possible to take a series of 50 originally designed for high speed photography instantaneous photographs on a circular using a film camera for recording images, it is now rotating plate. He suggested that when a almost exclusively used for recording Schlieren images sensitive enough film is developed, pictures Palflash 501 High Intensity, Illuminance Pulsed Flash in conjunction with CCD and CMOS digital high speed of such subjects as a man walking, a dog’s tail Light Source (The Cooke Corp., USA) cameras. The link for triggering the Palflash501 wagging, and the movement of horses and and the digital cameras is made via digital delay other animals could be recorded. generator and computer software. Motivated by trying to satisfy wagers (as The market for the Palflash 501-driven in the case of California governor Leland Schlieren imaging systems is still very similar Stanford’s challenge that all four feet of a to the customer base of the original film horse are off the ground while it is galloping camera/Argon Spark based systems. These — photographed by Eadweard Muybridge include universities, aerospace companies, in 1872) to purely academic reasons (as Schlieren image, onset of detonation phase (G. Simard, defence companies, government departments in the case of the development of the Mechanical Engineering, McGill University, Canada) and many others. A Palflash 501-based Electrical Tachyscope, the forerunner of Schlieren imaging system can be used for modern stroboscopic photography, in 1887), fuel injection studies for automobile and over the next 60 to 70 years photographic aero engines, missiles and ballistics studies, instrumentation and specifically high speed wind tunnel based studies and many more photography made numerous advancements. applications. There were several advances in the early The Palflash 501 open spark light source and 1930’s. Dr. Harold Edgerton developed the its predecessors have now been around for Stroboscopic Flash System, which provided Schlieren image, high speed compressible turbulent deflagration wave (G. Simard, Mechanical Engineering, more than 150 years. During those years it has extremely short duration light sources to stop McGill University, Canada) action and give a detailed look at sequential events. This system was evolved from a very crude unit which captured an image of a spinning used in conjunction with still photographic equipment to produce newspaper to the Palflash 501 with its digital camera companion that a series of photographs superimposed on the same negative. Prime can take Schlieren images of events with speeds in excess of 3000 m/sec. The only differences separating the Palflash 501 from its predecessors examples of the use of this system are the photographs of hummingbirds taken by Dr. Edgerton and the series of sport photos that Gjon Mili are the application of modern electronics and optics. The Palflash 501 Schlieren light source can be truly said to be the thoroughly modern provided for Life magazine. There are three main types of lighting used in Schlieren imaging application of a timeless technology. systems: Xenon & Mercury continuous short arc sources, typically CONTACT used for applications where the subject movement is very slow or Steve Daicos, President almost stopped; Xenon strobes, used for relatively fast applications E-mail: firstname.lastname@example.org 2009 | WIND TUNNEL INTERNATIONAL
The Fight for Efficiency and Accuracy in Wind Tunnel Testing The introduction of new data acquisition and control systems, plus a master computer program has brought significant improvements in measurement quality (accuracy and repeatability) but also progress with testing efficiency, flexibility and data delivery at the Aerodynamics Center of RUAG Aerospace. By Andreas Hauser, Head of Aerodynamic Engineering. 78
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In order to fulfil those needs RUAG Aerospace is constantly improving its wind tunnel equipment, using mostly internal knowhow and experience, with notable achievements in the last four years. In 2005, new data acquisition (DAE) hardware was introduced. Additionally, the old control systems (COSYS, COntrolled SYStems used, for instance, for model manipulators) were replaced with up-to-date hardware, new control software and intelligent user interfaces that allow quick reactions to incoming test results. The latest step was completed in 2007 with the commissioning of the new in-house-developed wind tunnel Master Control Software (Master Computer Program, MCP) that provides overall control over the test and measurement sequences. A sketch of the environment in which these upgrade activities took place and the systems which were affected is given in the figure [below]. It shows the relations between the MCP, the COSYS (such as model manipulators and wind tunnel controls), the DAE, the experimental facilities and the test objects (wind tunnel models) in the context of the associated technologies and RUAG’s capabilities.
Data Acquisition (DAE)
Dassault Falcon 7X (scale 1:8.5). Low-speed wind tunnel tests for stability & control as well as for aero database definition.
n commercial wind tunnels such as in RUAG Aerospace’s
facility in Switzerland, customers range widely: from aerospace and automotive to civil engineering and sports, etc. Consequent testing needs differ greatly. In fact, not one test setup is exactly the same as the other and often customer-specific equipment is necessary. The efficient and manageable implementation of all the different customer needs in one single facility requires specialists from a number of fields (such as electronics, mechanics, sensor technology, software and testing) plus a high degree of flexibility in the wind tunnel and its equipment, be it mechanical, electrical or software. What all customers have in common is a need for accurate and repeatable results, obtained at a high productivity level, so that a maximum return can be obtained within the often severe time and budget constraints.
2009 | WIND TUNNEL INTERNATIONAL
The success of a wind tunnel test depends considerably on the availability of a high-quality data acquisition system, able to resolve with great certainty the minute force variations sensed by the instrumentation. The Aerodynamics Center is relying on the MGCplus technology of Hottinger Baldwin Messtechnik (HBM) for data acquisition tasks in its wind tunnels (with the exception of static pressures where PSI pressure scanners are used). The system offers a choice of different amplifier types which, when combined with the proper connection boards, enable meeting the highest accuracy demands of a wide variety of sensors. Concurrent, dynamic measurements at sampling rates up to 2,400 Hz can be performed with this system. For each of RUAG’s wind tunnels, the hardware components have been integrated in a cabinet together with various monitoring devices. To comply with ISO-9001 standards, periodic calibrations are necessary for the entire measurement chain. In a high-tech wind tunnel environment, downtime must be minimized, as costs per time unit are rather high due to the intrinsic substantial assets and operating costs. Therefore a special on-site calibration system/ procedure with traceability to national standards was developed. The system is certified in accordance to RUAG standards for calibration of HBM equipment and is also available as a service for external customers. 79
Airbus A400M full model (scale 1:15), equipped with high power hydraulic engines for accurate thrust simulation.
“Not one test setup is exactly the same as the other and often customer-specific equipment is necessary. Efficient and manageable implementation of all the different customer ... requires specialists from a number of fields ... plus a high degree of flexibility in the wind tunnel and its equipment.”
Controlled Systems (COSYS)
Master Computer Program (MCP)
Increased demand for use of our upper and rear model support systems from passenger and transport aircraft development programs as well as UAV and fighter projects triggered the initiation of an internal development project to replace the old control systems for these model manipulators. BMW production-car development The main goals were: to add (scale 1:3 or 1:2.5) for drag reduction and driving stability tests. flexibility in programming motion sequences; to improve control with respect to precise speed management on non-linear axes; to introduce the possibility for synchronisation between the different manipulators; and, in addition, to enhance the interfacing capabilities not only with the operators (man machine interface, MMI) but also with the other wind tunnel systems and in particular with the Master Computer Program (MCP).
At the heart of the new capabilities is the Master Computer Program. It controls the wind tunnel, data acquisition (through the DAE) and model motion (through the various COSYS systems) and interfaces with the test engineer. No product available on the market was able to fulfil all of RUAG’s requirements so the Aerodynamics Center’s own software group was put to work on the development of a new MCP. The resulting tool provides a high degree of flexibility and the in-house development allows short reaction times when special capabilities need to be implemented – a clear added value to our customers.
The system is operated from two PC-based user interfaces (MMI and AP-Player) and a real-time control system. The MMI (man machine interface) is primarily used during model installation and removal. It provides manual control of relative and absolute single axis movements on all available axes in both the actuator and the model-based coordinate systems. With the AP-Player (AP: Ablauf-Programm, position sequence), it is possible to load, store, program and run automatic motion sequences with any number of synchronized model axes. A teach-in feature of the APPlayer is especially useful to copy a manually obtained position into the current sequence. While running through a position sequence on the AP-Player, the user can also – additively – influence the motion of the selected axes through the MMI or an interface to the master computer. This feature can be useful when several manipulators are used in parallel and exhibit different deformations due to loads and still must be geometrically and temporally synchronized. The software is based on National Instruments’ LabVIEW real-time programming tool and is designed to allow easy and straightforward inclusion of additional axes and model supports.
The new MCP is designed to run on commercial of-theshelf hardware and uses Linux as an operating system. It features an architecture which allows easy integration of new components, such as data acquisition systems, control systems for novel model manipulators, or data processing modules such as wind tunnel correction algorithms. Due to its scalable architecture only system immanent limitations (CPU-speed, memory-size, etc.) affect its performance; by distributing software modules on different computers in the LAN, bottlenecks can easily be avoided. For dynamic testing synchronicity over any number of different data acquisition systems with potentially different sampling rates is implemented via accurate time stamping of the measured signals, thus allowing straightforward time-correlated analysis even over the boundaries of the different data acquisition systems (e.g. values from balances from the HBM and pressure values from the PSI systems). An easy-to-use graphical user interface helps the wind tunnel operators to safely and efficiently control and monitor the test. At the same time, customers get a comprehensible overview of the
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“Customers get a comprehensible overview of the incoming results allowing quick decisions on the test procedure.”
Athlete wind tunnel tests. In this case drag reduction on a skeleton driver.
incoming results allowing quick decisions on the test procedure. A key milestone was achieved during the test phase in RUAG’s EWTE (Experimental Wind Tunnel Emmen) where the interactions of the software modules were tested under real world conditions but without the pressure of a commercial test. Finally, in
November 2007 the new wind tunnel software system was officially released for a first production wind tunnel test in RUAG’s LWTE (Large Wind Tunnel Emmen) and had to prove its worthiness under productive conditions. Beside normal performance tuning no significant problems were encountered. Now, the MCP and the associated tools are
not only utilized in the Center’s wind tunnels but whenever measurements need to be performed on any of the other test rigs (the balance calibration rig, for example). The introduction of the various new components (DAE, COSYS, and MCP) have brought significant improvements in measurement quality (accuracy and repeatability) but also progress with regard to testing efficiency, flexibility and data delivery. Our wind tunnel operators appreciate the new possibilities of the systems and, even more importantly, our customers are well satisfied with the high quality of these services offered by the Aerodynamics Center of RUAG Aerospace. CONTACT Andreas Hauser, RUAG Aerospace E-mail: email@example.com
PALFLASH 501 High Intensity,
Illuminance Pulsed Flash Light Source Specifically Designed for Dynamic Schlieren Imaging Features ■ Sub µsec duration flashes from 250 to 750 nsec ■ High discharge energies, 2 to 24 joules per flash ■ High frequency of repetition to 1 µsec minimum between pulses ■ Schlieren, widely varied collimation and UV optics ■ Small discharge (point source) size
Applications ■ Dynamic Schlieren Imaging ■ Shadowgraph Image Analysis ■ Flow visualization ■ Ballistics and Detonics ■ Spray Particle Behavior Imaging
1 µsec 250-750 nsec
6930 Metroplex Drive Romulus, MI 48174 Tel (248) 276-8820 Fax (248) 276-8825 firstname.lastname@example.org www.cookecorp.com
Keeping Ahead of the
Pack One year after Windshear unveiled the most accurate wind tunnel in the world, the Concord, N.C. company continues to lead the way in its industry.
i n ds h e a r i s t he first commercially available wind tunnel of its type. Windshear offers the advantages of a full-scale rolling-road wind tunnel with boundary layer management, temperature control and uniform aerodynamics and is primarily aimed at serving the wind tunnel testing needs of auto racing teams. Those teams include top competitors from Formula One, NASCAR and IndyCar racing divisions. The goal is to provide a more level playing field for all teams, regardless of their size, looking to maximize aerodynamic performance. Windshear has already made adjustments to help teams reach that goal, and continues to strive to give clients the best testing experience possible. “We are always looking at new approaches, and ways to make the data even more valuable to our clients,” said Jeff Bordner, Site Manager at Windshear. “We have a state-of-the-art facility, but we want to continue to be ahead of the pack in the wind tunnel industry.” That kind of mindset has helped Windshear own one of the most visible wind tunnels 82
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in the world. Four Formula One teams visited Windshear in the first six months after its opening and used its detailed testing capabilities to gain valuable insight on how to make their machines perform at peak levels. Those teams aren’t the only ones to find success. Many topflight NASCAR teams have taken advantage of the Windshear facility since September and others are lining up to use it. More than 95 percent of Windshear’s schedule was filled by last summer, as racing teams spent countless hours using the Windshear facility. The full-scale, single belt rolling wind tunnel is a one of a kind facility, giving those teams the kind of precise data that teams need to succeed. IndyCar teams have also come to Windshear for tests, taking advantage of its flexible scheduling and vast databases. NASCAR teams in lower divisions – many based within 2009 | WIND TUNNEL INTERNATIONAL
30 minutes of the Windshear facility – have also come to experience the 22-foot high wind tunnel fan. Those customers can also see the ways that Windshear is constantly striving to better its product. The company recently enhanced its wind tunnel with a new product launch, a temperature compensation system. That system eliminates the need for up to two-hours of warmup, creating more productivity for race teams and sparking a 20 percent increase in testing throughout. Later this year, a second improvement comes on-line with the implementation of a system to measure force at the wheel. That creates a new level of extremely accurate aerodynamic side-force measurement. All of that design work helped Windshear win the Professional MotorSport World Expo 2008 Award for “Testing Technology of the Year.” “That award reflects the kind of commitment we have at Windshear,” Bordner said. “We are proud to get such recognition, because it reinforces our approach in how we do things.”
Getting into the game The first Windshear customer came in June 2008. That Formula One team spent several days testing at Windshear, and opened the door for other teams in other racing divisions to learn about the powerful capabilities of the Windshear wind tunnel. Windshear held its official grand opening July 18, 2008 and more than 300 racing and local officials marveled at the kind of impact the new facility could create. But creating the world’s most accurate wind tunnel wasn’t a breeze. 84
The groundbreaking for the $40 million complex began in April 2007, and construction was completed in January 2008. But Windshear officials – establishing their brand for accuracy and excellence - spent the next six months undergoing a vast commissioning process. That included calibration, testing its own cars in the tunnel, and preparing for outside customers. But all of that work has paid off – creating a wind tunnel that separates itself from the pack because of the purest testing results a customer can attain. By March – three months before Windshear’s first customer – more than 75 percent of the available time at Windshear in 2008 had already been reserved. A fixed-floor wind tunnel creates a boundary layer of friction that skews results, incorrectly simulating real-world aerodynamic conditions. But Windshear’s revolutionary full-scale rolling wind tunnel eliminates that resistance thanks to its moving ground-plane, providing the most accurate data of any wind tunnel in the world. Test vehicles are placed on the rolling road and tested at speeds up to 180 miles per hour. Windshear’s main fan features 5,300 horsepower, and the rolling road accelerates from 0 to 180 miles per hour in less than a minute. The wind tunnel accommodates full-scale vehicles, and has temperatures controlled to within plus or minus 1 deg F. The hightech rolling road is 10.5 feet wide by 29.5 feet long. The “road” is actually a continuous stainless steel belt just one mm thick, and it is designed to last up to 5,000 operational hours. If a vehicle remained on the belt the entire 5,000 hours, it would “travel” approximately 186,000 to 248,000 miles. During testing, “through-the-belt” sensors WIND TUNNEL INTERNATIONAL | 2009
based on certain environmental factors. “We know the importance of testing gas mileage in vehicles,” Bordner said. “We want to become a primary location for the Environmental Protection Agency to turn to for those kinds of tests.” The wind tunnel may also be utilized by Top Fuel dragsters down the road, and that could create another captive audience for this innovative track. The proposed USF1 Formula One team is also stationed near the Windshear wind tunnel, and that team may be able to use the Windshear facility to make an impact in its inaugural season on the circuit. The Windshear site can operate 24 hours a day, and Windshear officials are optimistic that they can double their current staff and the amount of available time for testing in the future. “We have a lot of different prospective avenues that can be used to utilize our facility to its fullest potential,” Bordner said. “We have Where does Windshear go from here? The wind tunnel has numerous other capabilities, and officials hope to plans for a big year.” capitalize on them. The Windshear wind tunnel can be a vital tool for CONTACT the environment, because it allows the testing of vehicles to see what Jeff Bordner kind of gas mileage they can get, and how to maximize the mileage E-mail: email@example.com measure the aerodynamic down force under each tire. All that data might help a team succeed, but how can they keep such sensitive material from getting to their competitors? Windshear uses absolute confidentiality with all of its clients, and offers several ways to keep such testing as secretive as possible. All test data files are erased from Windshear servers once a customer’s testing is complete. The Windshear facility is also physically configured so that no two racing teams will see each other’s vehicles at any time. Also, all Windshear employees and contractors sign secure nondisclosure agreements and are bound by privacy guidelines. Card keys are issued to all customers, limiting areas and times of access, and unauthorized personnel are prohibited from customer areas. “Security is one of our biggest priorities,” Bordner said. “We want to make sure all the data collected by our clients does not leak out. Our practices and policies ensure that.”
Innovative PIV Systems
Flow Field Analysis in gases and liquids Multi Phase Flows: microscopic and endoscopic 3D PIV and High Speed PIV Tomographic PIV LaVision GmbH Anna-Vandenhoeck-Ring 19 D-37081 Goettingen / Germany Tel. +49 551 9004 0 Email: firstname.lastname@example.org www.lavision.com
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5/20/2009 2:16:33 PM
Laser Sheet projected across wind tunnel model Source: DLR Goettingen
velocity snapshot The real-time measurement of the velocity flow field in a wind tunnel can be achieved in many ways. Dr Callum Gray of LaVision Inc. reviews historical and current methods and makes the case for Particle Image Velocimetry which has many enthusiastic supporters in the aerodynamics community
ind tunnels are used to study
the effect of air flowing past a stationary object and the most basic kind of test applied in a wind tunnel is the measurement of aerodynamic forces and moments on model aircraft and automobiles using transducers and balances. The gross response of any model in the wind tunnel to different conditions of air speed and direction provides accurate insight into how a similar object will respond in the real world. Empirical design iterations in one of the earliest wind tunnels provided the Wright Brothers reliable parametric data for the design of the first heavier-thanair vehicle. The process of wind tunnel testing has not altered fundamentally from that time although detailed aerodynamic data obtained through the use of flow 86
measurement and visualization is used for better-informed design iterations. Wind tunnel testing can be seen as the reality check between design inspiration and aerodynamic reality but has also served to accelerate a fundamental understanding of aerodynamics and the non-linear interaction between air flow and object. In addition, the parallel refinement of computational fluid dynamics schemes by validation with experimental data provides a predictive capability by simulating flow conditions
and model response without having to physically test each and every case. Measurement of aerodynamic parameters such as air pressure, flow velocity and direction are the key to improving computer models which will ultimately result in fewer iterations and more efficient wind tunnel testing. Pitot tubes, multi-hole probes and micro holes provide detailed insight into the distribution of forces near the model and across its surface. Pressure Sensitive Paint (PSP) applied to a model surface and imaged by a suitable device can provide continuous surface pressure distribution. Besides pressure, the air velocity around the model can be measured to construct a more complete understanding of the flow field. Basic flow measurement has been achieved by observing and measuring the direction of tufts of yarn attached to a model surface at key locations. Flow visualization of smoke streams or bubbles also reveals basic flow structure
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to aid interpretation of force and pressure measurements. Quantitative techniques such as Constant Temperature Anemometry (CTA) and Laser Doppler Velocimetry (LDV) measure precisely the time fluctuation of velocity at a point and have provided accurate quantitative values for refinement of numerical models such as Large Eddy Simulation (LES). Different tools for measuring aerodynamic velocity have specific advantages and disadvantages. CTA has the primary advantage of resolving rapid fluctuations in the flow to resolve microstructures but intrudes into the flow and requires cumbersome calibration. LDV is an optical technique and apart from requiring tracers in the flow to reveal its motion, does not affect the flow being measured. The disadvantage with both of these point techniques however, is that they can only be implemented simultaneously at a few points with limited ability to measure and characterize instantaneous flow structure. Two or more point velocity probes can sample velocity simultaneously at different locations to resolve flow-length scales by correlation analysis and physically scanning a point probe through a flow field can reveal the time average flow structure. Instantaneous flow structure can be measured using Particle Image Velocimetry (PIV). PIV is an image-based measurement technique for mapping the instantaneous velocity structure in gases and liquids and has been used extensively in the wind tunnel environment for both
Schematic of PIV image recording and subsequent image analysis using cross-correlation
basic research and as an aerodynamic design tool. PIV provides a quantitative “snapshot” of a velocity field and provides unique insight into flow structure unavailable by point measurement techniques. The current state of PIV technology allows images to be acquired at frequencies up to 10KHz and so may also resolve the time evolution of flow structure. PIV provides unique and intuitive insight into aerodynamic flows but also has substantial practical and economic advantages for collecting data in the wind tunnel environment. Extensive velocity data can be collected within a short measurement
Is available to view online ENT AND NEWS, COMM
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A PIV Vectormap of a vortex in air showing vector arrow array and derived vorticity
PIV velocity data plotted with pressure sensitive paint data Source: DLR Goettingen
time window allowing data to be acquired under continuous and optimal flow conditions. Also, the total time for PIV setup and data acquisition is short reducing the cost of running expensive wind tunnel facilities. The ease and speed of data gathering can make detailed comparisons between experimental and numerical models possible with even a few seconds of captured data. The origins of PIV can be traced back to the simultaneous work of several researchers in the late 1970â€™s developing what was termed Laser-Speckle-Velocimetry (LSV). Initial experiments were rudimentary and proved the principle of quantitative flow mapping for very low velocity flows and a small field of view. The principle is very simple. Neutrally buoyant tracers are introduced into the flow just as with LDV but typically at higher 88
densities. A laser sheet is introduced into the region of the flow that is of interest and an image of the illuminated tracer particles recorded by a camera viewing normal to the light sheet. Pulsing the laser sheet two or more times allows the flow to transport the tracers between pulses the image of the displaced particles provides a record of the flow velocity. The local point displacement of the tracer particles across these photographically recorded images was originally measured from the fringe pattern generated by passing a low power laser beam through the film. Early examples of LSV utilized a high concentration of tracer particles such that they simulated a continuous surface within the fluid. Later research showed how a reduced density of particles achieves higher reliability, spatial resolution and accuracy. Resolving individual tracer particle images was an important requirement and thus the technique came to be known as Particle Image Velocimetry (PIV). Technical development of PIV has progressed scientifically and technically to provide higher fidelity and more extensive velocity data in less time. Motivated by a scientific interest in the kind of data that PIV provides and facilitated by technologies developed in other fields, PIV has developed in its approach and
has adopted several key enabling technologies. State-of-the-art CCD imaging sensors were utilized in the 1990â€™s and high frame-rate CMOS sensors in the last decade. Evaluation of PIV images is now performed digitally utilizing fast Fourier transform (FFT) based cross-correlation techniques to extract particle displacements and performed in real time on multiprocessor desktop computers. Compact, high-energy, double-pulsed, solidstate lasers provide precise and efficient illumination and timing of laser pulses onto successive images thereby permitting the direction of the flow to be resolved. Photographic recording did not permit this directly. The sensitivity of modern sensors and the high energy of PIV lasers mean that wind tunnels may be seeded lightly utilizing a submicron droplet generator using non-toxic, light oil which evaporates leaving no persistent trace in the measurement volume. Integrated software suites have been developed to provide image acquisition, image processing, post processing and data visualization. International special interest committees of experts such as EuroPIV, SmartPIV and PIV Challenge have established a degree of standardization in the methodology and analysis techniques in PIV as well as providing a forum for current and future development of the technique. Almost all flows of engineering interest have significant components of velocity in three dimensions. The basic PIV technique as described measures the projection of two components of velocity. Accurate measurement of the two components of velocity parallel to the light sheet and the component normal to the light sheet can be measured by utilizing two cameras each viewing the light sheet at an oblique angle to the laser sheet. The measured two components of displacements from each of the camera perspectives are combined by triangulation to resolve three components of velocity. This extension of the PIV technique is termed Stereo PIV: as well as resolving the third component of velocity, it also results in improved accuracy of the two components of velocity in the plane of the light sheet. Stereo PIV is still restricted to velocity measurement across a plane defined by the laser sheet. Recent advances in flow mapping have led to further enhancement of the basic PIV technique to provide three-component velocity data through a volume. By expanding a standard PIV pulsed laser to fill a volume within the flow the illuminated particle cloud is recorded onto three or four cameras. As with Stereo PIV, each camera views the illuminated particles from a different perspective. However, rather than measure WIND TUNNEL INTERNATIONAL | 2009
two dimensional displacements from each of the projections of the particle cloud, the image data from all of the cameras is combined using a Tomographic algorithm to create a virtual threedimensional intensity distribution in a computer. The three dimensional array of intensities discretized over voxel embodies the positions of all the particles within the illuminated volume. In a manner completely analogous to the two dimensional crosscorrelation used in planar and stereo PIV, a three-dimensional Tomographic PIV data of a vortex in air showing volumetrically cross-correlation is used to resolved velocity information interrogate the virtual seeded volume to for hugely improved insight into complex flows. Additionally spatial derivatives of the resolve 3D3C velocity data. The use of cross-correlation avoids the need flow field can be calculated in all three spatial to identify individual particles and match them dimensions. With Planar, Stereo and Tomographic to their displaced position and thus allows the system to operate with a high concentration PIV experimental aero engineers have the of seeding particles. This technique is termed possibility of characterizing complex, unsteady Tomographic PIV and, although conceptually flows in wide variety of research areas quickly more complex than its planar PIV cousins, and comprehensively. Rotorcraft and fixed is a direct extension of the PIV technique. wing research utilizes PIV to characterize It’s clear that the fundamental advantage of transient flows for unique insight and for Tomographic PIV is that it reveals the complete validation of a variety of flow models. Civil topology of unsteady coherent flow structures engineers utilize the technique to measure
interior climatic flows and flow interaction between model buildings. High-performance auto vehicle testing incorporates PIV at every level from noise and drag reduction through exterior flows and even investigation of the flow within the engine itself. Aero acoustic research utilizes PIV systems with KHz repetition rates or in a phase-locked mode to determine the relationship between the flow and the acoustic field that drives or derives from it. Basic research into turbulent structures and boundary layers depends directly on PIV to provide instantaneous turbulent length-scale information and insight into the interaction of flow structures. Even research into the flight of animals, insects and birds has been driven in recent years by PIV measurement. There is no doubt of the effectiveness and adaptability of PIV and its variants in the wind tunnel and there are a substantial number of experienced and enthusiastic users of this technique in the aerodynamics research community. CONTACT Dr Callum Gray, LaVision E-mail: email@example.com
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A wind tunnel in an engine test cell
Formula 1 Grand Prix racing is as closed a community as exists outside the military and defence industry. Technical breakthroughs — particularly on testing techniques — are scrupulously guarded. But did you know that F1 teams, in effect, take wind tunnels to their engine test cells to simulate on-track conditions? In this article Schreiber, Brand u. Partner Ingenieurgesellschaft mbH (SBI) gives us a fascinating glimpse inside the world of F1 technical development
ind tunnels are one
of the most fascinating test facilities in the automotive industry. This includes the engineering of the tunnel itself, as wind tunnels can be structured to address different task fields, each with its special requirements and characteristics.
Figure 1. Schematic of air-conditioning and pressure system which supplies air to engine test cell below
We normally think of wind tunnels in the following contexts: • Aerodynamic wind tunnels for production vehicles with requirements in flow quality like cp-distribution and buffeting • Aeroacoustic wind tunnels for production vehicles with the need for low background noise level WIND TUNNEL INTERNATIONAL | 2009
• Aerodynamic wind tunnels for race cars with quite special requirements for boundary layer conditions • And climatic wind tunnels for production vehicles with special requirements with respect to air temperature, air humidity, snow and rain simulation. Only a few people know that there are other aerodynamic applications in operation; even some aerodynamic “insiders” are unaware that they exist. Every high performance engine test cell needs a combustion air handling unit in order to supply conditioned air for the combustion process of the engine. In racing cars, additional aerodynamic changes need to be accommodated to address the increased air pressure in the engine airbox inlet at high speed. The system described here combines the usual air conditioning demands with high dynamic transient aerodynamic demands. In other words, it supplies conditioned combustion air at constant conditions into the engine test cell with an outlet velocity in front of the airbox inlet following a vehicle racetrack velocity profile in real time. It is an important tool used in the racing car industry and in Formula 1 engine testing. The power development of a non charged engine is beside other important factors influenced by the density of the air locally in front of the suction inlet. As the density is a function of the ambient pressure, humidity and temperature, it is of high importance to simulate (see Figure 1) these physical circumstances according to the different local race track conditions across the world. In detail the power development
S Y S T E M I N T E G R AT I O N AERODYNAMIC FACILITIES ENGINEERING
PRODUCTS • Wind tunnel • Dynamic pressure simulation • WT-control-system • Aerodynamic components SERVICES • Engineering • CFD simulation • Upgrading • Commissioning • Facility management WALLNER und BRAND INGENIEURGESELLSCHAFT mbH An der Tuchbleiche 29-31 68623 Lampertheim - Germany
of an internal combustion engine will be calculated with the following equation:
In a fixed engine some of the important variables are pL, TL and RL. The air temperature TL and the relative humidity expressed in the gas constant RL are simulated by the air conditioning unit. The pressure pL is a sum of the ambient pressure and the local dynamic pressure in front of the air box inlet. The ambient pressure of course varies from day to day but the simulation of the dynamic pressure is
SERVICES • Civil engineering • Architecture • Supply systems • Mechanical engineering • Process engineering • Test-rig engineering • Aerodynamics / Aeroacustics • special tasks: • • •
Vibration engineering Noise protection ( BImSchG ) GENERAL DESIGN
TEST-RIG ENGINEERING BUILDING & SUPPLY SYSTEMS fon +49 6256 8301-0 fax +49 6256 8301-789 www.wbi-online.de
SBI WTI| Annual Review.indd 1 2009 WIND TUNNEL INTERNATIONAL
SCHREIBER, BRAND u. PARTNER INGENIEURGESELLSCHAFT mbH An der Tuchbleiche 29-31 68623 Lampertheim - Germany
fon +49 6256 8301-0 fax +49 6256 8301-789 www.sbi-online.de 24.08.2009 17:22:03 91
“The power of an engine running full throttle at 360 km/h with and without face velocity simulation leads to a difference of…approximately 30 kW (40 hp). This influence is not negligible”
Figure 2. Dynamic pressure versus vehicle velocity
Figure 3. Simplified pressure profile at 83 m/s; free field conditions
possible with this kind of air handling unit. As a result the specification of a modern combustion air conditioning unit needs to define a capability not only to condition the air temperature within a tolerance of +/- 1 deg C and the relative humidity within a tolerance of +/- 2,5 percent rH, but also to supply this air with a face velocity between 80 km/h (50 mi/h) and 360 km/h (224 mi/h) following the race track profile – and all this in real time. Comparing the power development of an engine (see Figure 2) running full throttle at 360 km/h with and without face velocity simulation the local pressure difference due to the dynamic pressure of approx. 6000 Pa (0.87 psi) at a temperature of 20 deg C leads to a difference of approx. 6 percent – or approximately 30 kW (40 hp). This influence is not negligible for the mapping of a top high performance engine. More than 80 percent of the local temperature and humidity values at the different race tracks across the world are covered if a combustion air system is able to achieve temperatures between 18 deg C and 45 deg C and relative humidity between 10 and 80 percent (or 5 g/kg to 20 g/kg). As the shape of the airbox inlet influences the pressure distribution in the duct downstream, the pressure distribution over the face of WIND TUNNEL INTERNATIONAL | 2009
SBI Figure 4: Graph 3 CFD simulation of a nozzle flow facing a simplified airbox
Figure 5. Lap simulation with combustion air system
the inlet gains importance. In consequence, the supply flow quality has to be as close as possible to the real track conditions. To achieve the closed possible simulation (see Figure 3) in the test cell, it is important to find a good compromise in space requirements and simulation result. CFD is a good tool to optimize the ratio of nozzle and air box inlet to a cost effective size (see Figure 4). With regard to the transient behaviour, the physical latency of the flow velocity to the real vehicle velocity is of high importance. Even at possible accelerations of up to +15 m/s² (+49.2 ft/s2 or 1.5g) and decelerations of up to – 35 m/s² (114.8 ft/s2 or nearly 3.6g), modern air handling units can follow the dynamic race track profile with a latency of less than 250 ms. Under special conditions it is possible to reduce the latency to zero. A small section of measuring data for a real time race track velocity flow simulation inside the engine test cell is attached (see Figure 5). Due to confidentiality reasons it is not possible to show more details or the whole lap but the graph indicates closeness with which flow velocity follows the required velocity (equivalent to the vehicle velocity on the track). CONTACT Stefan Becker, SBI E-mail: email@example.com
Whatever you need to measure in your wind tunnel, bustec should be your solution
bustec combines nV accuracy with hundreds of MB data-throughput and online real-time monitoring with continuous data storage bustec – the leader in High Precision Data Acquisition and Signal Conditioning
US, tel +1 (760) 751-2049, fax +1 (760) 751-1284, email: firstname.lastname@example.org Bustec Inc., 1507 East Valley Parkway Suite 3-412, Escondido, CA 92027 Europe, tel +353-61-707 100, fax +353-61-707 100, email: email@example.com Bustec Ltd., World Aviation Park, Shannon, Co. Clare, Ireland.
bustec.com Bustec |HP 0909.indd 1 2009 WIND TUNNEL INTERNATIONAL
28/08/2009 12:38 93
Rotor testing set-up in front of wind tunnel
In today’s world, the Aerospace and Test industry has high economical demands for the development of its products, with the need to produce very fuel-efficient planes a primary driver. Structural, as well as engine, designs are pushed to limits not known before. These demands translate, on the one hand, to short development cycles and, on the other hand, to the request for very high measurement accuracy to verify new designs. These economic demands are changing the world of data-acquisition and Test & Measurement leading, in turn, to two main challenges. The first is measurement accuracy and the second is real-time storage and online monitoring. Dr. Fred Blönnigen, CEO of Bustec, a leading supplier of highperformance data-acquisition and test products explains
ur products are all based on computer- needed to monitor the data online in real time and store all data independent and open-platform standards. They continuously onto a RAID system. One of these systems was provided by Bustec to AgustaWestland, a offer the highest density available in the market and have brought modularity to a new level. global leader in designing helicopters, for the optimization of rotors. Its Typical applications range from airframe, jet- system consisted of 128 channels, each sampling with up to 216KHz, plus some slower measurement and control channels. These channels engine and rocket testing to wind tunnel applications. Within this experience, let’s take two recent examples of wind tunnel consisted of Digital Inputs and Outputs (in total 96 channels) as well data-acquisition systems. What both companies needed was a solution, as some slower channels for measuring pressures and temperatures which could provide them with the possibility to acquire all channels (in total 120 channels) plus a couple of analog control channels and simultaneously with a sampling rate of up 216 kHz. In addition they 8 fast counter channels for the rpm of the rotor. 94
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The better modern Analog-toDigital cards can deliver 100dB SNR, a performance demanding a good cabling infrastructure. With twisted-pair differential cables, full advantage of the extreme low noise levels of 1 to 3 µV Bustec cards provide can be taken, thus giving you a total error in the 10mV scale of around 0.05 percent. With the accuracy of their systems and the large databandwidth, Bustec can address the economic demands for shortened test cycles and can deliver results which let customers achieve their design goals. With cables being expensive and susceptible to noise, the request for many small distributed and synchronized data-acquisition and test systems is becoming more and more prominent. A logical candidate would be standard Ethernet to connect these distributed data-acquisition system design. In complete data-acquisition system is shown above: at the top are the boxes. But Ethernet hasn’t addition for these The Signal conditioning units, with the data-acquisition rack and the input/ Picture of been able to fulfill the needs of large applications, output cards below and the RAID system at the bottom large dataacquisition system synchronization down to large parts of the calculations have to be done the order of a couple on powerful digital signal processors (DSPs) directly in the data of nano-seconds (10-9 acquisition systems. seconds). Bustec’s systems provide a perfect fit for those requirements. The industry has Large systems consist of 19-in (48-cm) rack enclosures solved this by introducing a with up to 12 “motherboards” per mainframe with new standard, called LXI (Lan powerful DSPs, local memory and an onboard eXtension for Instrumentation). programmable voltage reference for “on-the-fly” LXI is a standard all major calibrations. With this approach, Bustec provides Test & Measurements companies its customers with the possibility to do a complete are adopting. Bustec supports these “end-to-end” calibration of the whole system in less than half a The LXI efforts and believes product based on second and without the need to unhook the cabling. For the different based ProDAQ 6100 measurement requirements, Bustec provides different function (input this new standard provide the user, in this case the aerospace companies, and output) cards and up to eight function cards can be fitted to each a real advantage in cost as well as in performance. of the motherboards. These racks are scalable and can be stacked. Therefore Bustec is releasing its new line of LXI products. The product Each of these mainframes can hold up to nearly 5000 channels. is called ProDAQ6100 and houses four of our generic function cards. Another important factor is the analog accuracy you can achieve with Being based on standard 1Gbit Ethernet with TCP/IP stacks, they are the data acquisition equipment provided, including the sensors and, in by definition build for distributed systems and are connected to a particular, the cables. Good cabling is especially important, meaning customer’s workstation or server via standard 1Gbit switches. They twisted-pair shielded cables, not the widely-used BNC cables: they provide the same advantages already present in former Bustec systems, simply aren’t good enough for the today’s requirements. With BNC namely accuracy and data-bandwidth. Furthermore they give the user cables, a signal-to-noise ratio (SNR) of 70dB is the maximum you can the same “on-the-fly” calibration possibilities. achieve and BNC cables tend to pick up noise levels of over 1mV (a It doesn’t come as a surprise, that having answered to the main quite normal occurrence in industrial environments). While this may request of industry, Bustec is becoming more and more successful in be acceptable when measuring 10V signals, it certainly is not if your the Aerospace Testing Industry and in the Wind-tunnel facilities. signal is the order of 10mV, a normal voltage for bridge measurements. CONTACT In this case, a noise level of around 1mV translates into an error of 10 Dr. Fred Blönnigen, CEO, Bustec E-mail: firstname.lastname@example.org percent. This is neither acceptable nor desirable.
The other system was sold to a Helicopter development center in Jingdezhen, China. This system was even more demanding, with the need to monitor and store 448 channels simultaneously, each channel sampling at 102.4 KHz. These requirements are quite normal, even in large systems with several hundred dynamic and/or several thousand static channels. But it serves to illustrate that the bandwidth with which data can be collected and concentrated on one or several different servers and workstations is a crucial aspect of the
2009 | WIND TUNNEL INTERNATIONAL
Advance of Technology Across the diversity of wind tunnel facility types and their test missions, the one constant is the relentless advance of technology. In all areas of wind tunnel testing, yesterday’s technology simply will not satisfy today’s test objectives. Dr. Steve Arnette, Vice President, Jacobs Technology Inc. provides a perspective that cuts across the various industries that utilize wind tunnels. test vehicle. Contrast this unsteady plenum flow with the smooth streamlines that slip around the vehicle on the open road at the same distance and it’s easy to appreciate the challenge associated with creating the “open road” within the open-jet plenum.
Jacobs technical services span the design, build, operation and maintenance of advanced test facilities and analysis using state-of-the-art computational methods.
utomotive companies prefer to test in wind tunnels having open-jet
test sections, primarily because they offer lower background noise and a semi-anechoic environment for developing vehicles with improved wind noise performance. The conventional wisdom is that aerodynamic compromises are required, due in large part to the complex interaction within the plenum test chamber between the free shear layer surrounding the jet, the plenum chamber, and the collector at the rear of the plenum that ‘collects’ the jet back into the wind tunnel circuit. If you’ve ever had the chance to stand in the downstream corner of an open jet plenum (out of the flow, of course!) and experience the flow yourself, you can believe in the need for aerodynamic compromise. The flow is highly irregular, with transient secondary flows, low-frequency buffeting and the like. In the typical open jet plenum, this location is approximately 5 to 10 m (15 to 30 ft) from the rear corner of the 96
One of the most significant of these aerodynamic compromises is an adverse pressure gradient. Data published in the open literature shows that most open-jet test sections used for automotive testing exhibit the characteristic of increasing static pressure in the rear of the test section. The resulting horizontal buoyancy manifests as an artificial reduction in the vehicle’s drag – the drag force measured in on the wind tunnel is lower than the actual value on the open road. This has been a given for open jet wind tunnels realized over numerous decades – until now. BMW’s new ATC tunnels in Munich are the first to break through this barrier with an advanced design that provides a constant axial distribution of static pressure. This unprecedented level of simulation fidelity provides BMW cost, quality, and efficiency benefits for their product development process (see related article in this issue). Our team at Jacobs is proud to have collaborated with BMW in achieving this breakthrough, which came as the result of an intensive R&D program involving the latest in computational and experimental methods. The United States government is continually upgrading its wind tunnel facilities to keep pace with next-generation technologies, many of which hold the status of national assets due to their critical role in developing military and civilian aircraft. The investment in new one-of-a-kind, highspeed data systems to support advanced rotorcraft testing at the Arnold Engineering Development Center (AEDC) National FullScale Aerodynamic Complex (NFAC) at NASA Ames Research Center in California is a great example.. NFAC is a unique wind tunnel facility that includes both 24.3 x 36.6 m (80 ×120 ft) and 12.2 x 24.3 m (40 × 80 ft) test WIND TUNNEL INTERNATIONAL | 2009
sections for full-scale testing. The new data system, which is built around Jacobs Test SLATE software, allows up to 2000 data channels to be collected at sampling rates up to 65 kHz. The cumulative data rate exceeds 20,000,000 samples per second, and the system has a time resolution of 300 nanoseconds to allow physical measurements to be correlated to fine angular resolution of rotor position. Researchers are now furnished with a volume of simultaneous data never before available, enabling studies of new advances in rotor technology with advanced concepts such as active independent blade control. The system collects a tremendous amount of raw data during a test, raising the legitimate question of “How long does it take to extract useable information?” As a test engineer will tell you, more data doesn’t necessarily translate to more insight and there was legitimate concern about translating this tremendous data capability into better test results. This rotorcraft testing is of interest to the U.S. Army, U.S. Air Force and NASA researchers and all collaborated during the project in defining what engineering results were needed from the data. As a result of this concerted effort to define the ultimate output of the test (and not the technical features of the data acquisition system), Jacobs was able to tailor the system to provide solutions, and not just piles of data. The solution includes advanced data re-sampling algorithms that interrogate data streams to obtain parameters of interest, and calculate important results (e.g. aerodynamic coefficients as a function of time and correlation coefficients between variables of interest) in real time as the test is executed. For a standard test involving some 17,000,000 measurement points across the many data channels, the system then provides the test team with a final report, including all calculated results of interest, within one minute of concluding the test. Having this type of real-time insight, as opposed to intensive posttest data analysis, allows test plans to be modified and optimized in
2009 | WIND TUNNEL INTERNATIONAL
real-time. Any test engineer will tell you the results of the current test are the most valuable piece of information in defining the next test. Unfortunately, the time lag between test and useful results for traditional data systems doesn’t afford this luxury. The new system at the NFAC facility breaks through this barrier. Advanced rolling road systems have become a fixture in modern automotive and motorsport wind tunnels, but there is perhaps no more dramatic recent application than the Windshear facility in North Carolina. It is the first full-scale rolling road wind tunnel in North America and is optimized for automotive and motorsport testing, with special features for both NASCAR and open-wheel racing cars. Such a rolling road system is required to achieve the stringent simulation accuracy needed to optimize the all-important underbody aerodynamics for racing cars. The Windshear facility offers a top speed of 180mph, with the result that tests can be conducted at track Reynolds number. The facility is now in continuous operation, providing a level of simulation and data quality previously not available in wind tunnels for hire. It is interesting to note that Windshear’s very first commercial customer attributed the mid-season turnaround of their NASCAR racing program to their work in the facility. Confidentiality restrictions preclude additional detail, but this example highlights how properly utilizing such a test facility can translate directly to competitive advantage. As these snapshots illustrate, there is no ‘steady state’ with respect to wind tunnel technology. For those who contemplate the future replacement of wind tunnels with computer simulation, this is an important realization. Just as computer technology progresses, so too does the wind tunnel. Regarding computer technologies, recent advances reflect a large concentration in enhancing “useability” and speed. The former
Similar Jacobs examples of physical testing and computer simulation from the aerospace industry.
“Our team … collaborated with BMW in achieving this breakthrough, which came as the result of an intensive R&D program involving the latest in computational and experimental methods” comes in the form of increased ease of grid development and post-simulation data processing, where there are now multiple commercially-available software tools. The latter has taken the form of increasing parallelization, where codes are becoming more and more adept at utilizing a large processor count available from either a single supercomputer or a cluster of many, smaller machines. A parallel computing capability is now a standard feature for all commerciallyavailable CFD codes. On the other hand, there have been relatively few recent developments for the actual solver technology. It is for this 98
reason that recent developments associated with the CESE method (Conservation Element Solution Element) are receiving intense scrutiny within CFD circles. At Jacobs, Dr. Joseph Yen has led the development of a parallel CESE code. The technical advantages of the code are significant. It is inherently transient, lending itself to simulation of transient flow phenomena. This is important because essentially all problems of interest are transient. Take the example of the flow over an automobile which, in many important ways, is governed by the flow in the wake downstream of the body. The wake is inherently transient and unsteady, highlighting the difficulty associated with steadystate flow solvers, and examples from aerospace applications are the same.
At a detailed level – which becomes more important as we strive for incremental improvements that enhance system performance, whether it is for the competition of a racing series or the larger competition of the global economy – the problems of interest are typically governed by transient flow phenomena. Second, the code is inherently applicable to both low-speed and high-speed flows. This is an important breakthrough, as the standard approach of the last several decades has been to utilize codes tailored to either incompressible or compressible applications. The result is that most commercially-available codes are tailored to low-speed applications, and most codes dedicated to highspeed problems are maintained by government researchers. The CESE method is equally applicable to incompressible and compressible flows, and the Jacobs code has been applied with strong success to applications ranging from the flow within an open jet plenum chamber (as discussed above) to the supersonic exhaust of a rocket engine. Third, the code is capable of resolving small disturbances – both small-magnitude (such as sound waves generated by the low-speed flow around an object) and small length scale (such as the sharp discontinuity that occurs across a shock wave). This is why the method has displayed such promise regarding aero-acoustic phenomena, enabling a direct simulation of generated acoustic waves, and has simultaneously shown strong promise for systems involving complex, transient shock/expansion interactions. Given its success in simulating real-world systems involving both low and high speed flows, it seems safe to say that the CESE method will play a prominent role in the future of aerodynamic investigations. The examples summarized above highlight progress for both wind tunnels and computational simulation methods. There is of course strong interest in the
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“We believe both physical testing and computer simulation will play a prominent role well into the future, and that the two will become more integrated over time” future roles of physical test and computer simulation, and much of the discussion assumes the future will see one dominate over the other. At Jacobs, we’re proud to help our clients improve the quality of their product testing and analysis methods, whether this takes the form of designing and constructing test facilities that offer improved simulation features; improving data acquisition systems to provide more useful results from a test; enhancing computer simulation capabilities to provide a more realistic simulation of real-world behavior; or even providing on-site test facility operations and maintenance services built around best practices proven to optimize throughput and efficiency. We pride ourselves on supporting clients in developing, realizing, and utilizing the technology solutions that drive their product research and development (R&D) and test and evaluation (T&E) activities. We believe both physical testing and computer simulation will play a prominent role well into the future, and that the two will become more integrated over time. This is the sort of general statement that no doubt leaves the reader asking for a more specific answer. We don’t profess to have all of the future answers, but I do think that current activities at the United States Air Force (USAF) Arnold Engineering Development Center (AEDC) provide a great example of what form this integration might take in the future. AEDC is the most comprehensive collection of aerospace groundtest capabilities in the world, encompassing 58 different test facilities including large-scale wind tunnels, propulsion test facilities, vacuum chambers capable of simulating the environment of outer-space, and various high-energy facilities. At AEDC, where the cost of testing at supersonic speeds is significantly higher than anything required in the largely-incompressible world of automobiles, computer simulation is a valuable tool for optimizing the design of test programs. Jacobs is proud to support the USAF on-site with the engineers, scientists, and technical staff that conduct this work. Computational simulation provides guidance on the “points of interest” in a test program, allowing, first, test resources to be concentrated on those portions of the operational envelope that require the most intense scrutiny and, second, the optimum design of instrumentation to obtain the information required from a test. At AEDC, the norm is for test and evaluation (T&E) to include both physical test and computer simulation. There are no doubt other examples in other industries, but it is striking that AEDC has adopted this approach as its normal mode of doing business. A similar integration of physical test and simulation along this line of “optimum design of experiments” seems a logical development for all industries that rely on the wind tunnel as a critical tool. Instead of “test vs. simulation”, we believe the future will be dominated by “integrated T&E” in which the whole is greater than the sum of the two parts of physical test and computer simulation. As illustrated by the examples cited here, it is also clear that the “steady state” of the future will not be fixed, but will instead take the form of a relentless advance of technology – for both physical testing and computer simulation. CONTACT Steve Arnette, Ph.D. E-mail: Steve.email@example.com 2009 | WIND TUNNEL INTERNATIONAL
Win with Southampton World-leading aerodynamics & aeroacoustics wind tunnel testing, research and development at the University of Southampton. Clients include UK Sport, Ferrari A1GP, Airbus, Formula 1, America’s Cup, World Rally and LMP teams...
www.windtunnel.soton.ac.uk Photo: Southampton Photographic
About the Airbus Wind Tunnel in Filton • Working section: 12 ft x 10 ft (3.65 m x 3.05 m) • Flow speeds up to M 0.26 (197 mph) • General test speed: M 0.20 • Turbulence level 0.15% • High and low pressure air systems (3500 psi and 280 psi) • PSI 8400 pressure system (>1200 pressure tappings)
Airbus in the UK’s state-of-the-art wind tunnel has tested commercial and military aircraft, including the A400M.
• 6 component under-floor load cell balance
Airbus Wind Tunnel
Spreading Its Wings Beyond Aviation
A large low speed wind tunnel with low operating costs offers a cost effective solution to aerodynamic design and validation
hen you walk into the BAC1-11 and Concorde to the A320, A330, over the last five years in upgrading the wind tunnel at Airbus’s A380, and now Airbus’s newest aircraft — fan and gearbox, adding a flow straightener site in Filton Bristol, the A350 XWB. and screens, upgrading the main balance to UK, the sense of history Led by a 12-person team of multi-skilled, load cells, adding a new control room and is overwhelming. The world-class specialists, some with more than modernising the data acquisition and control facility, which recently celebrated 50 30 years of experience in testing, the facility systems used in both the wind tunnel and years of operation, has played a part in has grown into a state-of-the-art facility. models. The result is a leading-edge operation the development of aircraft from the VC10, Several million pounds has been invested that can support current and future needs. 100
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From simple to complex testing, Airbus does it all
are supplied in collaboration with external companies, but the facilities are modified to accept these techniques with the minimum of impact on time and cost. Customers have been pleased with the service they’ve received. “It was a wholly positive experience,” according to Cobham Mission Equipment. “Every customer we’ve had has praised us for our flexibility,” says Alex Liberson, Tunnel Maintenance and Development Engineer. “We do everything we can for our customers.”
“We’re continually evolving the capability of the people and this facility, and therefore can offer customers a range of services from the very, very simple, to the most complex,” says David JohnsonUnique testing Newell, head of Wind opportunities available Extensive testing in Airbus’ wind tunnel in Filton, UK, resulted in an ecoefficient, quiet A380. Tunnel Operations for The Filton facility is unique in many of its Airbus in the UK. offerings. One is the ability to perform tests of Open for business internal combustion engines, both scale-model Now, following facility and process “We can offer just blowing wind over a and full-size versions. improvements that have expanded model, to a full range of data acquisition “Most test facilities don’t offer this service, but capability and brought test times down tailored to the customer’s need. Having we have the health and safety controls in place from typically two month to three the right blend of skilled technicians on for this,” explains David Johnson-Newell. This weeks, Airbus is spreading its wings site enables us to react to our customers is also very useful in and opening the doors to its high-tech, needs very quickly, and having control over all of assessing cooling low-cost wind tunnels for business. and performance Customers ranging from lone athletes our systems means they issues in a controlled looking to improve their speed through can be adapted quickly environment. better aerodynamics to multi-national without recourse to external An extensive and companies seeking validation for new suppliers.” Alongside the regular secure workshop equipment such as long-endurance is also offered on unmanned aerial vehicles (UAVs) can in-house measurement the site, as is design now benefit from the use of Airbus’ wind of forces and pressures, and manufacturing tunnels and its test teams for periods s y s t e m s h a v e b e e n d e v e l o p e d f o r t h e Airbus’s state-of-the-art wind tunnel features Carbon Fibre capability (including ranging from one day to one month. Fan blades manufactured by Lola Cars International. They a world-class rapid The team has already welcomed measurement of internal rotate at up to 400 RPM and are over 7 metres in diameter. prototyping facility). its share of non-aviation related model balances and strain They can also test customers. Things designed to improve gauges, model anemometry Tu r b i n e P o w e r the environment, including wind systems, accelerometers Simulators (T.P.S.). turbines and solar panels, have passed and the motorisation of through the doors — a testament to the components, again in company’s dedication to improving eco- pursuit of testing efficiency. See what efficiency throughout every industry. Airbus also has the Airbus has Olympic-class athletes have brought capability to perform engine to offer prototype equipment such as skis, face rake measurements at The Filton facility’s cycles and more. Military customers a range of test conditions. sister site in Bremen, A 12-person have brought equipment so secretive, Nearly all the techniques are run test team Germany, is also opening its doors to other the test team’s bosses weren’t allowed concurrently, reducing the number with 30 customers. It’s smaller, but offers a similar years of to know what was being tested. of runs required, and therefore the experience range of measurement techniques. Industrial aerodynamics on items such cost. Advanced techniques such as ensures Both sites are available for interested test as oil rigs, buildings, and traffic signals laser anemometry and aero-acoustics accuracy. customers to meet the teams and tour the have also been tested. facilities. Potential customers will be able to The team even once talk with the wind tunnel specialists about services offered famously hosted their requirements and view the range of • From wind only to forces and pressures and other data acquisition Britain’s television capabilities on offer. (including acoustic measurements, strain gauges, component celebrity, Jeremy For more information about Airbus’ wind balances, accelerometers and anemometry) Clarkson, who was tunnel facilities in the UK and Germany, • Still and video image capture of flow visualisations testing how much please contact David Johnson-Newell. • LDA/PIV and other advanced measurement techniques supported wind it took to blow a • Test slots available from one day to one month; 8-hour or 12-hour person over (he took day occupancy CONTACT off at 93 mph). But • Data acquisition and control with NI LabView David Johnson-Newell, Airbus Tel: +44 (0)117 936 6371 team members can • Data processing with C++ configurable to any data format E-mail: firstname.lastname@example.org now welcome more. 2009 | WIND TUNNEL INTERNATIONAL
Cal Poly’s N+2 CESTOL airliner design during fuel efficient cruise, with slots retracted
Moving to the Next Generation:
Wind Tunnel Investigations of CESTOL Technologies California Polytechnic State University, San Luis Obispo, Cal., has been collaborating with Georgia Tech Research Institute (GTRI), Patersonlabs, Inc., and DHC Engineering to fulfill a NASA National Research Announcement (NRA) to develop and validate predictive capabilities for the design, aerodynamics, and acoustic performance of Cruise Efficient, Short Take-Off and Land (CESTOL) subsonic aircraft with a largescale wind-tunnel test. Rory Golden of Cal Poly, describes the creation of a highly complex wind-tunnel model to develop the concept.
he NRA was a three-year award; during the first year
the objective was to select and refine CESTOL concepts and then to complete a preliminary design of a large scale (8 ft span minimum) wind tunnel model for the wind tunnel test. During the second year, the large scale wind tunnel model design will be completed and manufactured, along with the development of the wind tunnel testing plan. In the third and final year, the large-scale wind-tunnel test will be conducted along with the completion of the predictive codes for the advanced powered-lift concepts. These codes will subsequently be validated with the gathered experimental data, which will then be processed and released to the scientific community.
Within the development of the wind tunnel model the focus was to keep a modular design that will accomplish all testing objectives at hand, and leave room for future growth, use, and research. This concept increased the complexity of an already advanced model. In doing so, Cal Poly selected Patersonlabs, Inc. from a list of manufacturers to design and manufacture the model, as being the most enthusiastic, informative, and cost-effective. The model was designed as a 100-passenger, N+2 generation, regional CESTOL airliner with hybrid blended wing-body and circulation-control wing (CCW) flaps. The engines were placed over-the-wing for both community noise reduction and increased powered-lift performance when coupled with the CCW flaps. The outer mold lines of the model were determined by a configuration that was developed by David Hall and refined by Cal Poly. 102
Fuel-savings and noise goals was a focus of the design as set out by the N+2 definition (expected 2020) metrics of a 25 percent reduction in fuel consumption and progress towards -52 dB lower noise levels than current generation aircraft. The wind tunnel model was sized by the NRA and the size of available wind tunnels, which scaled the model to a 10 ft span. Since the main focus of this test was on the acoustics and aerodynamics of the N+2 design, the testing plans did not require empennage control surfaces, leading the model to have a clean aft end. Keeping future research in mind, the model was designed to incorporate a removable aft end to allow for various different tail designs to also be tested on the model. The powered-lift system utilizes CCW flaps that incorporate both leading and trailing edge blowing and four different flap deflections (0°, 30°, 60°, 80°). The CCW flaps were designed using both experimental data provided by GTRI and computational analysis conducted by Cal Poly. Both leading edge and trailing edge blowing slots have adjustable heights and are fed by low pressure span-wise plenums that include flow straighteners, thermocouples, and pressure measurements. The engines are modeled using TDI’s Model 441B turbofan propulsion simulators (TPS), which have a five-inch diameter, twostage fan with a three-stage turbine. They are mounted above the wing, with locations determined by experimental aerodynamic and acoustic results from GTRI. Each TPS unit is capable of producing approximately 175 lb of thrust, and have removable aft nacelles for compatibility with different future designs. WIND TUNNEL INTERNATIONAL | 2009
Cut-away view of wind tunnel model with significant components
Both low and high pressure air regulation systems are located inside the model and are remotely actuated. The high pressure air is fed through the balance into the model, and the low pressure around the balance. Both pressure supplies employ bellows in the transition from non-metric to metric to negate any forces produced by the pressurized lines that would have a negative effect on data. To attach the model to the sting arm of the wind tunnel, a blade
attachment is used to decrease the flow interference caused by the sting. This blade also provides room to run pressure and electrical lines into the model up the aft end of the blade that is covered with a fairing. Patersonlabs, Inc. was responsible for the design of all the internal plumbing, instrumentation, pressure regulation systems, and structural layout of the model. The model is instrumented by a six-inch flow-through balance
Cal Poly Sting-mounted model with 70-element stationary array, 30° traversing microphone, and far-field acoustic measurements in the NFAC tunnel
The major objective of this project is the generation of an open collection of wind tunnel data along with the development and validation of predictive codes for the advanced powered-lift concepts of next-generation CESTOL aircraft for measuring the aerodynamic forces and moments. The model’s left wing is instrumented with 230 static pressure ports to measure the pressure distribution, eight dynamic pressure Kulites to capture acoustic characteristics, and a cross-correlation rake to measure boundary layer interactions on the blown trailing edge flap. The right wing and wing-blend are nickel-plated and not externally instrumented to keep the surface clean to perform oil interferometry, which measures local shear stress on the surface of the wing. There are nine thermocouples placed inside the right wing to measure the wing surface temperature for oil interferometry calibration. The National Full-Scale Aerodynamic Complex (NFAC) 40 ft by 80 ft wind tunnel was chosen to perform the nine week large scale wind tunnel test. The NFAC offered several benefits over other large wind tunnels across the country, with the most significant being: the 10 ft span model could be mounted on a sting which allows for cleaner measurements of the produced aerodynamic forces and moments; the tunnel could supply the high pressure air at the mass flow rate necessary to operate the CCW slots and the TPS units; the tunnel is large enough that the downwash created by the CCW flaps would not impinge on the floor of the tunnel thus enabling
more accurate aerodynamic and far field acoustic measurements; the tunnel is acoustically treated such that aerodynamic and acoustic measurements could be performed simultaneously; and the NFAC’s cost and schedule fit within Cal Poly’s time frame and budget. The proposed test matrix for the model includes calibrations while mounted on the tunnel’s sting-arm of both the model and acoustic instrumentation, static tests of all blown features on the model, a Reynolds number sweep, a dynamic pressure sweep, a TPS sweep, and a CCW sweep. After the completion of the preliminary sweeps, eight to ten critical test points will be identified from the experimental data obtained. During the critical test points all experimental instrumentation will be utilized. Acoustically, the farfield measurements along with a traversing 30° sideline measurements will be made. Also the facility’s 70-element stationary array will be placed under one of the TPS units to characterize the noise signature beneath the wing. The aerodynamic forces, moments, static pressure measurements, and unsteady pressure measurements will simultaneously be conducted. Following these tests, the model will then be inverted and the same critical test points will be repeated. Inverting the model offers
Cal Poly’s CESTOL design on steep approach with flaps deflected and blown slots deployed
WIND TUNNEL INTERNATIONAL | 2009
Sure, there are some things we can´t control.
Cal Poly’s next-generation CESTOL aircraft performing a short-field landing utilizing engine flow entrainment by circulation control flaps
several advantages in obtaining experimental measurements, these being: the oil interferometry will require less lighting in the large wind tunnel by having high power lights on the floor of the tunnel that can be more easily directed on the wing surface; the 70-element stationary array can be utilized to identify any hot spots created by the TPS units; and the smoke visualization will be easier to observe and record. Once the critical test points have been completed, the model will be returned to right side up and alpha (up to +20 to -5 deg.) and beta (+20 to -20 deg.) sweeps will be conducted at three different tunnel speeds. Only far-field acoustic measurements, aerodynamic forces and moments, and static pressure measurements will be conducted for this portion of the test allowing a significant number of test points to be investigated, thereby creating the data base for current and future CFD validation efforts. The major objective of this project is the generation of an open collection of wind tunnel data along with the development
and validation of predictive codes for the advanced poweredlift concepts of next-generation CESTOL aircraft. This research can be utilized subsequently to improve the capability of modeling these complex flows for future development. This effort will address the following topics: low-speed aerodynamic characteristics up to and beyond maximum lift via a combination of computational and experimental efforts; by doing so, obtain a more complete picture of the flow physics and acoustic characteristics of a low-noise hybrid wing-body aircraft; and, at the same time, provide noise signature modeling to analyze not just the noise generated by the vehicle, but also the noise footprint around the airport during takeoff and landing. In accomplishing this, the project will provide a very innovative and non-proprietary example of a highly complex windtunnel model, in addition to an optimized test plan, that can acquire large amounts of test data given limited tunnel time.
CONTACT Dr. David Marshall, California Polytechnic State University E-mail: email@example.com 2009 | WIND TUNNEL INTERNATIONAL
But with Werum’s and SEA’s Wind Tunnel Control System WTCS you will playfully control your measurements. No matter if you are planning to build a new wind tunnel or modernize an existing one: With its modular structure WTCS can be easily integrated into existing or planned structures. Independent functional modules ensure that additional measurement systems or other equipment can be integrated at any time. Based on its core functions for measurement and configuration data management, test sequencing and control as well as error management WTCS enables you to set up a control system that can easily be adjusted to different tasks just by slightly changing the system configuration. Feel the tailwind for your projects with WTCS. Successful installations with renowed European manufacturers
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Werum Software & Systems AG 21337 Lueneburg, Germany Tel. +49 (0) 4131 8900-0 firstname.lastname@example.org
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aircraft The origin of the wind tunnel testing is connected with aeronautics but it has been used in many other industrial areas for decades. The main goal is the same — to improve efficiency and performance — but the main value is in reliable information provided in early stage of the development at reasonable cost. Some examples of non-aeronautical testing missions and the associated facilities in VZLÚ Aeronautical Research and Test Institute are reviewed by Jan Cervinka, Milan Jirsák, Zdenek Pátek and Štepán Zdobinský.
BOUNDARY LAYER WIND TUNNEL
owadays aerodynamics has become a very important
part of product development in the automotive and railway industries. Aerodynamic measurements in the wind tunnel, which are carried out early in the development of the vehicle, provide valuable information about the future characteristics and can significantly reduce development and operation costs.
All forces and moments acting on the scaled model of the vehicle are measured, the drag and lift usually being of the highest importance. The side-wind sensitivity, which has significant influence on driving qualities and stability, is also studied. Testing of parts of real vehicles to verify functionality of various systems (e.g. cooling system) is also common.. Visualization, which helps to optimize the external shape to improve flow field around the body, is also very useful. This can be done using many techniques, for example Particle Image Velocimetry (PIV), smoke or magnesium emulsion. 106
“The boundary layer wind tunnel (BLWT) has been in operation at the VZLÚ since 1996.”
The boundary layer wind tunnel (BLWT) has been in operation at the VZLÚ since 1996. It was designed and constructed by VZLÚ in cooperation with the Czech Technical University in Prague. The working section part of the wind tunnel is of 15.6 m length and 1.8 x1.5 m cross section. The 1.8 m diameter fan is powered by a 55 kW DC motor and generates maximum wind speed of about 25
WIND TUNNEL INTERNATIONAL | 2009
Railway-station 1:250 (Salzburg, Austria). Wind action on platform roofs and on pedestrians
Testing of the cross-wind sensitivity of high-speed train
Laser beam visualization of flow field
m/s (90 km/h) above the boundary layer. Equilibrium boundary layers have been adjusted above three types of simulated terrain roughness gradually (agricultural, suburban and urban) consistent with proper Eurocode categories. Instrumentation of the facility has been extended and innovated throughout the years of BLWT operation, serving in the fields of building and structural dynamics and gas dispersion modelling. The hot-wire anemometer, pressure scanners, Irwin probes, 2D particle image velocimetry, hydrocarbon tracing and detecting system with flame ionization detectors are included as well as special means for visualization in highly turbulent flow. Three-dimensional positioning and the 1750 mm
turntable are PC-controlled. Static pressure along the test section is monitored at 14 sections and an optimal pressure distribution adjustment can be carried out by variations in the ceiling contour. The majority of applications in early years represented customer and grant-aid tests with aeroelastic or pressure models of buildings and bridges. More recently, this field has been broadened to include various aspects of building ventilation and inspection of pedestrian wind conditions for urban innovation projects. General questions associated with the last applications or with their measuring technology are also studied (e.g. the challenges of Irwin probe calibration or the
2009 | WIND TUNNEL INTERNATIONAL
Testing of cooling system on a part of a real vehicle
development of pedestrian wind comfort criteria corresponding to wind conditions in the Czech Republic). A series of case studies concerning gas dispersion have been carried out since 2000. They include emission spread from heating stations, the casual heavy gas release nearby built-up area or diffusion of flues and dust from an abandoned coal basin. The current scaling of simulated wind structure models is from 1:300 to 1:400. However, higher scale factors are available for special studies. Scaling as small as 1:1500 has been used for modelling of gas dispersion over distances up to 3 km or similar scaling used for investigation of local wind exposure on topographic model. Results from these tests are then used for model of building test in standard scale (convenient for pressure measurements, etc.) The model is exposed to non-equilibrium flow here, artificially simulating that obtained on topography. This has shown that the 107
VZLU Realistic housing estate scaled 1:400. Stacks of four heat stations are active (at the critical wind direction)
standard (flat) roughness field can produce such flow if a special obstacle, optimized as to its shape, magnitude and its position, is placed in front of the model. The ASCE manual No.67 “Wind Tunnel Studies of Buildings and Structures” has been used during the gradual extension of BLWT applications and has turned out to be an excellent working guide.
Side elevation of the VZLÚ boundary layer wind tunnel.
“A series of case studies concerning gas dispersion ... include(s) the emission spread from heating stations, the casual heavy gas release to a nearby built-up area or the diffusion of flues and dust from an abandoned coal mine”
Top sports require novel approaches for improving results – cycling is not an exception, especially in its road racing format and time trial. This is the reason for testing bicycles with or without riders in low speed wind tunnels. Tests at VZLÚ 3m Low-Speed Wind Tunnel, which is close-circuit and has an open test section with 3 m diameter, proceed close to real flow velocity, i.e. up to the 50 km/h, commonly reached during cycle races. The synchronization of flow velocity and roadrun velocity (i.e. wheels rpm) is assured and indicated to the racer. The bicycle with the racer is fixed on a small frame, whereas the wheels lean on rollers – somewhat similar to indoor training equipment, with the difference that there is no need to deal with racer’s stability. Part of this frame forms an electromagnetic brake, simulating racer’s loading due to pedaling. This unit is attached to the six component external strain gauge balance, measuring forces
Topography model 1:1250 comprising part of river Vltava valley affecting wind exposure on site of projected tall buildings (at the back)
WIND TUNNEL INTERNATIONAL | 2009
and moments. Optical instructions and information are displayed directly inside the wind tunnel in the racer’s vision angle, including, for example, the speed, drag force / drag coefficient and any instructions to follow. All data are recorded and interpreted according to customer’s demands. Typically, forces and moments, flow velocity, wheels rpm, crank arm cadence, racer’s output power and pulse, snapshots, videos are provided. The measurements are commonly focused on drag reduction, or comparison of equipment in term of drag behavior effects. Important variables that influence drag include the racer’s position and attitude, the wheel design, the width of the grip, the handlebar settings, the shape and material of clothing and helmet. One hidden difficulty is the need to hold on
at the desired position for a certain time at an adequate physical performance. Flow visualization, especially the smoke trace, is also employed as a development aid. Performance improvements in the order of up to several percent were typically achieved. All measuring techniques and testing facilities at VZLÚ are developed continuously to meet our user’s requirements. Generally,
however, our main focus is on increasing accuracy and productivity. Our gained experience has led VZLÚ to an expansion of its wind tunnel testing to support non-aeronautical industrial branches and other top-level sports. CONTACT Zdenek Patek, VZLU E-mail: firstname.lastname@example.org
“Important variables that influence (cyclist’s) drag include the racer’s position and attitude, the wheel design, the width of the grip, the handlebar settings, the shape and material of clothing and helmet”
yclist at VZLÚ 3m LSWT
Low and high-speed wind tunnel testing for affordable prices
Testing in 3m low-speed wind tunnel from 1900 EUR/day! V ý z k u m n ý
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2009 | WIND TUNNEL INTERNATIONAL
PACIFIC INSTRUMENTS NFAC Wind Tunnel â€” A technician unlatches the door built into one of the guide vanes of the 16-Foot Transonic Wind Tunnel at NASA Langley Research Center, Hampton, Virginia. The tunnel, one of dozens of research facilities at Langley, was built in 1939 and most recently renovated in 1990.
When Less really is More Regardless of the type of wind tunnel (blow down, shock tube, arc jet or continuous), data must be collected from multiple classes of sensors and the tunnel operation must be controlled. Historically, wind tunnel control, data acquisition and signal conditioning are separate systems. Further, the control and acquisition portions are separate processes that use separate measurement systems yet many of the measurements are common to both. Additionally, data acquisition may require multiple systems for different classes of transducers. There are significant advantages in using a single system with Digital Signal Processing (DSP) hardware and comprehensive software not only for both control and data acquisition but also for multiple classes of sensors. Scott Swinford, Vice President, Engineering, Pacific Instruments, Inc. explains
ndependent systems normally require dedicated operational and service personnel for each system. Independent systems also require duplication of sensors. Signals such as P0, T0, and pitot measurements are used for flow control as well as for data analysis. Pitch, yaw, and roll measurements are used to control model positioning and must be recorded for data analysis. Actuated model surfaces must be controlled and their position signals acquired to determine the aerodynamic configuration. Duplication of sensors increases the initial cost, installation cost and maintenance cost. The advantage of a single system is lower initial capital cost and reduced operating expense. The single system approach, assuming some software automation, also requires fewer personnel to operate and maintain. 110
Control Systems (CS) aside, Signal Conditioning and the A/D system are also often independent. This configuration requires additional connectors, cabling and support staff. It also has increased failure points associated with the cabling and independent hardware. Cali bration of the system is usually done independently; contributing to longer pretest run-ups, potential for different calibration cycles and longer data reduction times. A data acquisition system with integrated signal conditioning (DAS) reduces costs, failure points and operator training while improving measurement accuracy. Employing Digital Signal Processing (DSP), the CS and DAS can be implemented as a single, complete system. The DSP processes measurement data, derives and verifies control parameters and outputs analog and digital control signals to the control hardware. The combined system reduces the number of measurements, simplifies operation and requires less time spent on setup and pre-test calibration. Figure 1 is a block diagram of the historical wind tunnel using separate CS and DAS while Figure 2 shows a block diagram of a wind tunnel using a single system with DSP control. The lower complexity of the DSP based control shown in Figure 2 demonstrates the advantages gained by combining control and data acquisition into a single system Residing on the DAS backplane, DSP can improve CS response by reducing the latency of data being processed for control outputs. A powerful DSP processor can generate multiple control outputs, verify the reasonableness of the outputs and notify the operator of any out-of-limits conditions. A DSP can produce recordable data like any channel in the DAS. By recording derived parameters, WIND TUNNEL INTERNATIONAL | 2009
intermediate calculations and control outputs, the actions of the CS can be correlated to measurement data and the health of the CS may be determined. A set of algorithms is needed to filter raw measurement data, generate derived parameters and control signals, NFAC MSL Parachute — The parachute is the Mars perform e r r o r Science Lab chute. NFAC tested the development checking and output chutes and performed selected parameters qualification testing on the final MSL-chute design. The and control signals chute will slow down the to the DAS. These MSL-delivery article in the Mars atmosphere during a l g o r i t h m s a r e the delivery phase of the MSL-rover to the surface. normally included in the DSP control package. Each algorithm can interact with others by modifying common memory locations to flag other algorithms of needs for delays, set point satisfaction, etc or to share data. This allows the flow control, model position control, and model part actuation systems to remain in the intended
Pacific Instruments 0909.indd 1 2009 | WIND (Corrected) TUNNEL INTERNATIONAL
synchronization. Data for control and recording may come from a variety of sensors. Strain-gauge, load and position transducers are usually conditioned and digitized by signal-conditioning modules specific to the measurement type. Modules that include both the signal conditioning and digitizer have the advantage of not requiring as many interconnections of analog signals that can degrade the measurement accuracy. Once digitized, the accuracy of the measurement cannot be further degraded by noise, crosstalk or other analog phenomena. Most transducers will have floating outputs, that is, the output will not be connected to the case or surroundings and therefore ground through the model or wind tunnel structures. However it is not uncommon for a transducer to become NFAC UH-60 IBC — UH-60 rotor on the NFAC’s Large Rotor Test Articles during wind tunnel grounded and this test to checkout Individual Blade Control (IBC) functionality. Traditionally a swash plate is should not invalidate used to control the rotor blade motion as function of azimuth angle around the rotor shaft, which means that all blades see the same control as the swash plate is fixed-system. As measurements by the name implies, IBC put the control function in the rotating plane allowing blade control at creating ground loops various azimuth angles around the shaft.
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Figure 1: HIstorical Wind Tunnel Control and Data Acquisition
Figure 2: Wind Tunnel Control using DAS-based DSP
that induce measurement errors. This requires isolation of excitation power supplies that power the transducers. Then, if a transducer is grounded, it will not induce currents in the input circuits of other transducers. Isolating the excitation power requires multiple power supplies in the signal conditioning amplifier and enclosure in which it is installed. Many backplanes such as PCI, VXI and PXI do not provide multiple, isolated power sources and use switching power supplies that produce high levels of high frequency noise. Such conditions are not the most suitable for processing low-level transducer signals. Truly high-performance signal conditioning most probably will be powered by analog-type power supplies using a proprietary backplane that enables distribution of multiple isolated power sources free of any high frequency noise. Most wind tunnels use pressure scanners when a large numbers of pressure measurements are required. This usually results in a second DAS and software to control, calibrate, operate and record data from the scanners. Since data processing requires time-correlated data, a means must be provided to
correlate data recorded by the multiple systems. A flexible DAS software package can integrate multiple systems by recording data from the pressure scanners with data from other sensors. This is accomplished by pulling data, time aligning it with data from other measurements and recording to a single media. Likewise data may be imported from other third-party hardware that uses recognized and documented buses. Data from all sources may be displayed simultaneously in near real time and distributed over a LAN for viewing and recording by multiple consumers. A critical element of any CS or DAS is the software that sets up hardware, controls calibration and operation and records, displays and distributes measurement and control data. The software must have a comprehensive operator interface that is configurable for specific elements of individual wind tunnels. Many operators write their own software using languages such as C++ and Visual Basic. However dealing with the low-level operation of individual hardware elements such as signal-conditioning amplifiers, digitizers and pressure scanners is a daunting task that can require many man-months of programming time. A better solution is an Application Programmerâ€™s Interface (API) type of package. Using an API, the facility programmer can configure the Graphical User Interfaces (GUIs), DAS and CS operations to meet facility specific needs without knowing details of the hardware operation or programming requirements. They simply make calls to the APIâ€™s dynamic link libraries (DLLs) to accomplish the desired function. The DLLs may include hardware programming, calibration routines, data acquisition and recording routines, data displays and data distribution. The DLLs handle all of the low-level work leaving the programmer free to deal with issues specific to their facility. In a real-world application, use of an API reduced programming time from an estimated 12 man-months to just one. CONTACT Scott Swinford, Pacific Instruments Inc. E-mail: firstname.lastname@example.org
WIND TUNNEL INTERNATIONAL | 2009
The Pursuit of Operational Excellence in Wind Tunnels The Supersonic Tunnel Association was formed in the United States in 1954 to bring together engineers and scientists working in the then-new technology area of high-speed wind tunnel testing. “International” was added to the name in 1996 to better reflect the current worldwide makeup of the organization which now includes representatives from test facilities located in 15 countries (29 active member organizations in total). By Edward A. Becks, P.E., STAI President 2009-10
he original , and still
primary, purpose of the Supersonic Tunnel Association International (STAI) is the sha r i ng of i n for mat ion concerning high speed wind tunnel facility operation, instrumentation and test techniques. More recently, the scope has broadened to include compressible fluid mechanics research outside the more traditional areas of wind tunnel testing. From the beginning, member facilities of the STAI have believed that sound personal relationships are a valuable foundation for technical communication, and STAI semiannual meetings offer the opportunity to meet and to interact personally with wind tunnel peers worldwide.
The STAI is a very informal organization which is not incorporated and has no assets or legal status. There are no fees or assessments associated with membership, and the semiannual meeting costs are defrayed by a registration fee for each attendee. The STAI operates within the constraints of a Constitution which is revised periodically to reflect changes in the technologies or economics of wind tunnel testing and facility operation. Two principles are specified in the group’s Constitution which are central to the organization’s philosophy and which are rigorously adhered to. The first of these, which is intended to assure the vitality of the STAI, requires that a representative from each member organization shall attend a meeting, and submit a technical contribution, at least once within a period covering two consecutive meetings (thus once per year). These responsibilities for attendance and presentation are usually, but 2009 | WIND TUNNEL INTERNATIONAL
not necessarily, satisfied at the same meeting. Secondly, to assure the integrity of the STAI and to maintain an environment conducive to the free and open exchange of information, the unsolicited marketing of equipment or services by any member to any other member(s) at STAI meetings is prohibited. The two meetings conducted each year are usually held in April and October. Member organizations serve as the meeting host on a voluntary, rotating basis. The host organization is responsible for all meeting arrangements and a registration fee is assessed per meeting participant to cover meeting costs. Many past meetings were held in the United States, but since 1996 meetings have generally alternated between the US member facilities and one of our many International member organizations. International meetings have been held in Australia, Japan, France, Belgium, Canada, England, Sweden, Germany, The Netherlands, Italy, Russia, India, and Israel. The STAI seeks to maintain a geographical balance in the selection of meeting sites in an attempt to distribute, as equitably as possible, the costs associated with travel to meetings. STAI meetings are generally conducted over a two-day period of which a day and a half is devoted to technical sessions and at least a half-day is allocated for a tour of the host organization’s facilities. Presentations made in the technical sessions are relatively brief and
are encouraged to be supported by a written paper that would be considerably more detailed. Proceedings from the meetings are mailed by the host organization to those members not in attendance. Papers are distributed only to STAI members in good standing, and are not to be referenced in other publications (outside STAI). This restriction is intended to encourage the reporting of preliminary results from work in progress, the sharing of information not completely understood, and discussions of problems not yet solved. Presentations and papers are in English. Applications for membership by high speed wind tunnel test facilities to the STAI are judged by the applicant organization’s ability to make useful contributions to the STAI, with primary consideration being given to the quality of the applicant’s facilities and the technical quality of the work being performed. Applicants are required to submit information concerning their facilities and the work being performed for evaluation against these standards. There are no geographic limitations placed on membership. An applicant organization is also required to submit a letter from a responsible official formally requesting membership, agreeing to abide by the STAI Constitution, and in particular agreeing to support the STAI’s requirements for meeting attendance and technical contributions. This letter should come from someone within the organization with budget control and authority to approve travel to meetings and time spent on preparation of technical contributions, and who would, therefore be ultimately responsible for the organization meeting its obligations to the STAI. After a formal request for membership has been received and favorably evaluated by the Executive Committee of the STAI, the applicant normally will be invited to send a representative to the next convenient regular STAI meeting to make a presentation about their facilities and technical work, and to answer questions. The application is then voted on by the membership as specified in the Constitution. The next meeting of the STAI will be hosted by the Council for Scientific and Industrial Research (CSIR) and will be held in Pretoria, South Africa, from October 11-14, 2009. The Executive Committee welcomes all inquiries and invites the reader to consider application for membership if your test facilities meet the requirements specified above. Please go to the STAI website (http://stai.dnw.aero/) for more information on joining our organization. CONTACT Edward A. Becks, STAI President E-mail: email@example.com 113
60 cm recirculating wind tunnel; Syracuse University
Wind, water, thermal… and much more Engineering Laboratory Design, Inc. Is located in Lake City, Minnesota and supplies turn-key equipment installations for research and educational institutions and manufacturing industry worldwide, explains its President Sigurd W. Anderson
ngineering Laboratory Design, Inc. (ELD) designs and builds equipment for university, government and industrial engi neer i ng resea rch a nd test i ng laboratories throughout the world. Our products primarily serve investigators in disciplines of fluid mechanics and heat transfer. We also support researchers working in geology and biological sciences. ELD was established as a corporation in 1966. Early experiments with fiberglass laminates and composite structures led, in the late 1960’s, to serial production of small open-circuit wind tunnels. Our customers’ research interests have directed our exploration and development WIND TUNNEL INTERNATIONAL | 2009
36x48-inch aerosol wind tunnel; Clarkson University
12-inch wind tunnel; University of South Pacific, Fiji
60 cm. test section with six-component balance; EmbryRiddle University
Airfoil model (20 cm cord); Ohio State University
of larger, faster and more complex and varied wind-tunnel systems and related equipment. We have produced more than 200, Eiffel, Gottingen and Wenham tunnels with test-section dimensions up to 1.5 m (4.9 ft) and velocities to Mach 0.7. Unique ELD wind tunnel systems include designs for study of insect and bird aerodynamics, turbine cascades and vane cooling, wind-driven rain, ram-air turbine deployment, thermally stratified flow regimes, automobile wind-noise mitigation, spray nozzle pattern evaluation, aircraft component testing, boundary layer terrain and architectural modeling, electronic component thermal cooling, plant pollination by wind, ultra-low speed industrial hygiene aerosol dispersion, icing research, wind anemometer calibration and microphone wind noise mitigation. ELD also designs and fabricates water tunnels, open channels and 2009 | WIND TUNNEL INTERNATIONAL
wave flumes plus instrumentation and traversing systems and models. Projects currently under way include: • Oscillating Flow Channel - U.S. Naval Research Laboratory • Flow Visualization Water Tunnel - University of Maryland • Open Circuit Wind Tunnel - University of Buffalo • Matched Index of Refraction Flow Facility - University of Wyoming • Cascade Test Section – Ecole Polytechnique de Montreal You are invited to visit our web site www.eldinc.com for product and contact information. CONTACT Sigurd W. Anderson, Engineering Laboratory Design, Inc. E-mail: firstname.lastname@example.org 115
BMW model-scale testing using the full suite of MTS model support technologies Source: BMW Group
Five Key Technologies for
Large-Belt, High-Speed Rolling Road Wind Tunnel Testing The trend towards high-speed wind tunnels with large-belt rolling roads presents some unique challenges. Stuart Carver, Advanced Systems and Motorsports Business Manager, and Victor Senft, Lead Aerodynamic Systems Engineer, for MTS Systems Corporation of Eden Prairie, Minn. review the five key technologies that need to be considered in such a facility.
arge-belt rolling road systems large-belt systems are machined in large, provide several advantages gantry-style machining centers. Belts also fold for vehicle wind tunnel testing. to reduce shipping size. It is also challenging to design such large The pr i ma r y adva ntage is the ability to test full-scale machines for service. To simplify service, prototypes at higher speeds with a full, advanced large-belt systems use moving uninterrupted simulation of the underbody ground plane systems that can be lowered flow field, yielding deeper insight into from the test section into the basement with real-world vehicle performance. However, an integrated lift. This allows for simple with these advantages come unique belt changes and ready access to machine components. challenges. In terms of increasing testing precision with One challenge involves the logistics of manufacturing and installation. The frames large-scale prototypes at high speeds, rolling used in large-belt rolling road systems must road technology has recently undergone be extremely stiff, yet also light enough for several advances. Here are five features that transport. The largest systems require oversize every wind tunnel test facility should insist load transportation permits. New-generation upon with the system they specify. 116
1 Belt fly-height control capabilities Moving ground plane simulation is essential to the aerodynamic development of passenger vehicles. With an increased focus on the environmental impact of vehicle emissions â€“ and with the many alternative powertrain vehicle architectures under development â€“ there is a constant push to increase vehicle efficiency. This makes the study of air movement through the engine bay, around the wheels and under the vehicle critical. High-performance moving ground planes are capable of simulating these phenomena in a wind tunnel. Belt support system design is vital to moving ground plane functionality. Supporting the WIND TUNNEL INTERNATIONAL | 2009
weight of the vehicle through the rotating tires provides a region of high positive pressure on the belt, while the rear diffuser (and front wing sections of vehicles such as Le Mans prototypes or Formula 1 cars) provides a region of high negative pressure above the belt. Another example is model-scale aircraft aerodynamic landing studies. This often includes turbine engine thrust reverser simulation, which creates an extremely high negative pressure field next to an extremely high positive pressure field. The challenge lies in supporting both of these loads simultaneously. To maintain accurate aerodynamic simulation in such cases, it is important to keep the belt position flat and stable. With the latest rolling road systems, a constant belt height and position is achieved by supporting the belt on a film of compressed air pre-loaded with vacuum, an approach known in the industry as belt fly height control. Vacuum channels are located between the compressed air ports. Combined with the stiffness of the steel belt (see next section), this configuration supports a constant belt fly height, even when testing high-weight and high-downforce vehicles. All vehicles being tested can be run directly on the belt, allowing for high negative pressure above the belt and
Advanced belt tracking details for an MTS Rolling Road System
enabling through-the-belt force measurements. The compressed air film above the belt surface also reduces friction created by the moving belt traveling at high speeds, reducing steady-state power consumption of the drive motor.
motion of one of the rollers is controlled via closed loop feedback to track the steel belt consistently straight. The use of a steel belt varying from 0.5 to 1.0 mm thick (depending on the application) also benefits tracking, because steel stretches far less and is more stable than fabric at high 2 Advanced belt tracking and speeds, functioning similarly to steel belts stainless-steel belt Another major challenge with high-speed used in steel-belt radial tires. The steel is rolling road testing involves belt tracking. On welded with an advanced process to provide new-generation large-belt rolling road systems, an endless belt, and the roller surface is plated
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2009 | WIND TUNNEL INTERNATIONAL
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with a material to reduce wear. Such steel belts offer a service life up to 180,000 miles (300,000 km). Equipped with these advanced belt tracking measures and steel belt, stable belt operation can be sustained at speeds exceeding 180 mph (289.6 km/h). Rollers must also be carefully designed to accommodate a steel belt at high speeds. The roller diameter must be large enough to allow the rigid steel belt to bend around it. As rollers up to 1 meter in diameter rotate at up to 2000 rpm during high-speed operation, finite element analysis must be applied during design to ensure that the roller will withstand the high resulting centrifugal forces. Large disc brakes are incorporated at each roller corner to quickly stop the belt in an emergency. With the largest systems, two-piston calipers and large-diameter discs are used at each corner to stop a system running at 180 mph (289 km/h) in under ten seconds. Steel belts also allow vehicle tire forces to be measured through the belt. Custom load cells are located under the tires to measure vehicle weight and aerodynamic loads on each tire, and the load is transferred through the moving belt to the load cell. Automatic load cell positioners support a variety of vehicle track width and wheelbase configurations.
system and stationary building must be minimized. These horizontal measurements provide a more complete understanding of total vehicle losses. Combined with the throughthe-belt force measurement, the aerodynamicist is well equipped for optimizing vehicle drag and the desired vehicle lift or downforce properties.
5 Dynamic platform balance
3 Hexapod model motion and internal balance Model-scale testing involves accurately positioning the model in a sequence of varying ride height, pitch, roll and yaw attitudes. This can be enhanced using a high-stiffness motion control and internal measurement balance. To achieve this balance, the model is supported by a strut from the ceiling. The motion control is provided by a six degree-of-freedom (6 DOF) electric actuator hexapod, similar to hexapods used with aircraft flight simulator motion systems. The hexapod is located in the ceiling and controls vehicle position by moving the strut. This approach provides a stiff, high-natural-frequency connection to the model, yielding extremely precise positioning capabilities accurate to 0.1 mm. The remote hexapod and advanced digital control systems allow the model’s center of motion to be selected by the aerodynamicist, simplifying transitions between models. Benefits include highly repeatable data, along with the ability to study transient effects such as diffuser stall and hysteresis in racecars. The resulting stiffness also permits heavier passenger car models to undergo testing at higher speeds. For “wheels-off” model testing, a wheel motion system may be incorporated into the rolling road turntable and synchronized with the model motion system, providing discrete control of wheel toe, steer and camber angles during testing.
4 Horizontal force measurement and vehicle restraints Horizontal force measurement is also critical to the vehicle aerodynamicist, and several methods can be employed with advanced rolling road systems in this regard. One method involves instrumenting the restraints that hold the vehicle to the moving ground plane system, which measures the vehicle rolling resistance and aerodynamic drag. New techniques under development promise to further simplify the vehicle restraint connection and increase positioning accuracy, along with separating the rolling resistance and aerodynamic drag data. Another approach involves measuring the horizontal forces acting on the moving ground plane system. Since the vehicle restraints are also attached to the moving ground plane, this method provides a more direct measurement of vehicle aerodynamic drag alone, removing rolling resistance. Since the moving ground is installed in a stationary wind tunnel building, interactions at the interface of the moving ground 118
Example of an MTS platform balance
The latest five-belt moving ground plane systems integrate under-floor balances to measure aerodynamic loads. Small belts, referred to as wheel drive units, are located under each tire, and the wheel drive units and vehicle rocker panel restraints are attached to the under-floor balance. A center belt is attached to the turntable to simulate moving ground under the vehicle. The turntable also allows system rotation relative to the wind source for conducting crosswind studies. This balance must be stiff to provide a natural frequency of 4 Hz - 6 Hz for measuring dynamic loads. A vehicle tare system is used to offset the static weight of the vehicle, allowing the load cells to be optimized to measure aerodynamic loads only, without having to compensate for vehicle weight. The tare system is supported with hydrostatic bearings to reduce friction and hysteresis in the balance measurements. Some under-floor balance systems are also capable of precisely measuring dynamic loads. This capability equips aerodynamicists with new insight into vehicle performance, such as the effects of vortex shedding off the rear of the vehicle. By insisting on these features with the large-belt rolling road system they specify, wind tunnel facilities will be well equipped to precisely simulate real-world vehicle operating conditions at high speeds. Test engineers can be confident they’re achieving the highest levels of accuracy and efficiency possible, with a rolling road system that will provide precise, productive and reliable operation over a long functional life. CONTACT Stuart Carver, MTS Systems Corporation E-mail: email@example.com Victor Senft, MTS Systems Corporation firstname.lastname@example.org WIND TUNNEL INTERNATIONAL | 2009
Standard Bombardier C-Series Low Speed Model in ONERA F1 Tunnel
Accuracy, speed of development and innovation are all guiding principles at Tri Models Inc., as Chris Athaide, Director, Business Development explains
Boeing P8 Poseidon Icing Certification Model in NASA Glenn IRT
2009 | WIND TUNNEL INTERNATIONAL
he history of air vehicle
testing and models can be traced back to the mid-1700’s starting with the whirling arm, where a “model” was placed at the end of a rotating arm and flight characteristics were crudely measured. With the first wind tunnels arriving in the late 1800’s, a whole new era was born. Since those early times, much has changed, but in some respects, much has stayed the same.
The characteristics of the wind tunnel test models have always been a function of the tunnels that could test them, the fabrication techniques available to build them and the instrumentation that could measure them. From the early wooden hand-carved models, to the modern precision CNC-machined models of today’s world, the evolution of wind tunnel models has proceeded at a pace that paralleled that of the aircraft itself. In the modern age, the use of wood, plastic and fiberglass were still the norm as recently as the early 1980’s and similar techniques were employed on the actual aircraft. However, in the mid 1990’s, a metamorphosis began. 119
Historically, with a few exceptions, aircraft development programs lasted many years, and during that time, development testing and verification were two distinct phases. However, following the F-22/F-23 development, the onus was put onto air-framers to shorten the development cycle by reducing the amount of testing and to test earlier in the process to get more data into the designer’s hands sooner. This was the case in both military and commercial aircraft as the business-jet market exploded, regional-jet markets soared and large military competitions dwindled down to a few. The direction was clear – get to the market faster! To support this, wind tunnel model design and fabrication sources were pushed to reduce their cycle times while improving the quality and the functionality of the models. As aircraft technology has developed, so has that of the wind tunnel model. Tri Models Incorporated was established in 1972, with only a threeperson staff. Since then, TMI has grown into an international supplier of wind tunnel models and ground test hardware serving all aspects of the air and space market. Today, TMI employs over 100 people using the most advanced tools in fabrication, CAD, CAM, Analysis and Inspection. Supplying models and test hardware to over 550 companies since its inception, TMI has been a party to the evolution. We employ the latest technologies in all aspects of the process, resulting in the ability to create high quality models at reasonable prices within schedules supporting the short development cycles. What used to be an eightmonth wind tunnel model in 1995 is now a four-month project and, in fact, many are completed in two months or less. Our design staff, using the Siemens NX CAD as well as the NX FEMAP Analysis package, is able to turn a customer’s outer mold line (OML) into a preliminary design in a matter of days. Use of standard designs and techniques enable us to provide a design proven not only on the shop floor but in the wind tunnel itself. Including designs for direct load measurement (strain gauges) to remote drive systems, our designers use leading edge techniques and hardware to ensure not only an accurate model that can be built efficiently, but also one that reduces the testing costs while 120
Cessna High Speed Model
Cessna High Speed Model
FALCON FaCET Freejet Heat Sink Engine/Model in AEDC APTU Facility. Source: Arnold Eng. Development Center
WIND TUNNEL INTERNATIONAL | 2009
Bombardier C-Series ½ Model in ONERA F1 Tunnel
obtaining more data, faster. Starting from the ease of installation, to model change times, the design of the model is critical to the success of a testing campaign. Our CNC Programming and Fabrication staff, work together to provide highly accurate machined parts and assemblies using Master-CAM software. Using the latest tools and CNC mills, TMI is able to rapidly machine a wide variety of materials from the exotics such as Aermet 100, Aerojet Combined Cycle Inlet Model Titanium or maraging steels, to the ‘ordinary’ stainless steels and aluminum. As recently as 2000, customers would request large fuselages to be fabricated from fiberglass, a design going back to the 1940’s. TMI has convinced many customers that a CNC machined aluminum body is not only stronger, more accurate and repeatable, but also cheaper than its fiberglass counterpart. The use of the latest cutting tools, programming methods and CNC machines has allowed models to transition from design to assembly in record times without sacrificing quality. A recent model with over 800 parts including numerous slat, flaps, ailerons, elevators, rudders and all the accompanying deflection hardware, was designed and completed in under 4 months. Extensive measurements are taken to validate the quality of the model at both the detail part and the assembly level. Verisurf Software is used to program the Coordinate Measuring Machine as well as obtain, analyze and best-fit the data. Data is taken to support the completion of a model where each component falls within tolerance, 2009 | WIND TUNNEL INTERNATIONAL
as well as the entire assembly. The data provided to the customer is not only more accurate than in the past but the amount of data is an order of magnitude in volume. The customer is presented with a comprehensive overview of every aspect of the model at a level of detail that was previously unimaginable. The technology innovation in motors and drive systems as well as instrumentation, has also played a critical role in the evolution of models. Previously, only large models had remote drive systems as the motors and associated gearing to move and hold a control surface were fairly large. Recent innovations in small DC motors as well as in gear-heads, have enabled us to include a remotely driven surface in 75 percent of all models. Canards, tails, rudders, elevons, flaps, nose cones, air flow valves and even the entire model itself have all been actuated. These features are critically important when a customer is testing in a tunnel that charges $5,000 to $10,000 per hour. TMI has grown from the small ‘garage’ shop to the premier supplier of wind tunnel models and ground test hardware for the global aerospace community. From basic force and moment models and large halfmodels to the full-scale Boeing 787 Landing gear static test rigs, we can provide it all. We design and build icing/deicing certification test models, hypersonic heat-sink inlet/engine test rigs with fully functioning JP7 fuel systems, pulse-detonation engine test rigs and many other exotic hardware as well. CONTACT Chris Athaide, Tri Models Inc. E-mail:CAthaide@TriModels.com 121
The challenges of powered propeller test models For many years NLR (The Netherlands’ National Aerospace Laboratory) has been specializing in “smart” wind tunnel models. These models feature mechanisms for smart functions or instrumentation for smart applications and allow wind tunnel tests that otherwise would be very time-consuming or even hard to accomplish at all. Jan van Twisk, Department Manager, Engineering & Technical Services at NLR, reviews how these smart models provide the increased functionality that is not offered by straightforward conventional precision models. 122
WIND TUNNEL INTERNATIONAL | 2009
â€œNLR (is) in an ideal position to support the wind-tunnel model programs associated with the ... new-generation counter-rotating open-rotor (CROR) powerplant installationsâ€?
Propeller-driven low-speed wind-tunnel model of the Northrop Grumman E-2D Advanced Hawkeye Source: DNW
ypical examples of smart models are those with rotating systems like propellers/fans or rotor systems, models with remotely controlled parts like flight controls, models with special instrumentation like balances or dynamic pressure sensors, and cryogenic models. Of these areas, that dealing with . powered propeller simulation systems, both for singlepropeller and counter-rotating open-rotor testing, is currently of particular interest Although only a few new propeller-driven aircraft have been developed worldwide since the 1980â€™s, NLR has continued the development of the technologies required for wind tunnel testing with powered propeller models. These technologies concern the development of six-component rotating balances, low-weight propeller hubs with 2009 | WIND TUNNEL INTERNATIONAL
instrumented carbon-composite propeller blades, telemetry systems for data transfer, integration of the above with air motors within the (generally narrow) contours of the engine nacelle, massflow control units to manage the division of pressurized supply air across the model air motors, and low-reaction air bridges to cross the main internal model balance with pressurized air. NLR has used and improved these techologies for various propeller-driven wind tunnel models during the 1990s and 2000s. The experience developed has put NLR in an ideal position to support the wind-tunnel model programs associated with the renewed research in new-generation counter-rotating open-rotor (CROR) powerplant installations.
larger. Also, CF material allows tuning of the dynamic properties of the blades, if required. This gives more freedom of geometrical design. Finally, composite blades enable, without weakening the blade to any significant effect, the internal installation of instrumentation like strain gauges (to define blade bending and torsion) or unsteady pressure transducers (to acquire noise data) without affecting the outer geometry of the blade, thus not causing any aerodynamic flow disturbance. After many years of optimisation and standardisation of the design and production process, NLR has proven that these CF blades are of very reliable quality, and no failures due to aerodynamic causes are known to have ever occurred.
Rotating balances Propeller blades Some 20 years ago, NLR made the decision to design and manufacture the propellers for propeller-driven wind-tunnel models from Carbon Fibre (CF) material instead of metal (aluminium or titanium). This choice was made because of the many advantages offered by CF blades. First of all, the mass of CF blades is roughly one third that of titanium blades, reducing significantly not only the weight but also the centrifugal forces of rotating propeller blades. This enables propeller hubs to be made of light alloy, even with the high (up to 18000 rpm) speeds required for the multi-bladed propellers of counter-rotating open-rotor installations. As a result, these light weight propellers are an effective way to reduce the risk of mechanical vibrations in a propeller test rig. Furthermore, if for some reason a CF blade would come detached off the propeller hub, the resulting damage will be significantly smaller, both to the surrounding test facility as to the propeller test rig itself. The rotating balance will most likely survive this incident: with metal blades, it would, most likely, be damaged beyond repair. Secondly, CF blades can be designed such that they have an infinite fatigue life. Their response to resonance frequencies is significantly lower than metal blades, and their margin to mechanical failure significantly
NLR has been developing balances of various kinds for many years, and rotating balances for the last 20 years. Its standard concept is based on a hub-spoke-rim type with the balance connected to one side of the propeller hub, not interfering with the propeller blade feet, thus allowing the maximum diameter to be used as offered within the local contours of the engine nacelle. Originally a 2-component (thrust and torque) balance, it has developed into a full 6-component balance with high accuracy (0.25% FS) for the two main components (thrust and torque) and lower accuracy (1% FS) for the other four components. The balances are designed for infinite fatigue life, based on the specified expected aerodynamic loads, supported by a full stress analyses. Since a rotary balance is part of an overall rotating test installation, its natural frequencies of vibration will also be determined, both analytically beforehand and, as a check afterwards, by testing. Obviously, the connection of the balance to the hub is of utter importance, and is defined in close cooperation with the hub designer. With ample experience in the calibration of rotating balances, both static and dynamic, as well as with the data processing of the output signals, NLR supports customers in these areas when required. 123
like air bridges and mass flow control units. Also, NLR can supply the For single-propeller test rigs, data and power transfer from the “earth” required test equipment for calibration of Turbine Powered Simulators to the rotating propeller and balance, and vice versa, can be done (TPS’s) in an Engine Calibration Facility (ECF). through a set of slip-rings at the back end of the motor. Although this is a well known, reliable and relatively cheap solution, they Air bridges and Mass flow Control Units have disadvantages: they require Both hydraulic motors and air motors are lubrication and will wear, thus driven by a high-pressure medium (fluid or air) requiring cleaning and other which has to cross the main internal balance maintenance; and the maximum of the wind tunnel model, both for supply surface speed of the slip-ring is and return. This has to be arranged so that limited, which causes rpm and/or while sufficient flow is supplied to the motors, shaft diameter limitations. the six degrees of freedom of the internal The alternative is data and balance are guaranteed, but without the power transfer through telemetry, reaction forces of the compressed fluid or air which does not have any of these influencing the output of the internal balance disadvantages but is relatively in any significant way. The same is valid for the expensive. For certain applications Internal balance with two supply and return air bridges large differences in temperature of the supply though, such as shaft-in-shaft set-ups in CROR and return fluid or air. test models, it is likely that slip-rings cannot For this purpose, NLR has be used, leaving no alternative but to use developed air bridges of very high telemetry. The telemetry units are integrated quality, even for low speed testing. as efficiently as possible with the rotating Since the available space in the balances, both electrically, mechanically and centre fuselage of the wind tunnel geometrically. model is usually quite limited, the The telemetry system, which was developed air bridge and the internal balance by NLR in close cooperation with a telemetry shall be matched as a fitting pair. subcontractor for application in various recent They are usually considered as CROR test installations, provides all sensorwind tunnel equipment, owned specific signal requirements with parameters and supplied by the wind tunnel, 6-component, 2x4-spoke rotating balances such as the number of channels, excitation voltage, data points per although their interface with revolution, max sample rate, band width and filtering specified against the wind tunnel model is very project requirements. important and can be quite critical. For the division of the supply air across the engines of the wind Propeller model motorization tunnel model remotely controlled The drive for the propeller of a wind-tunnel model can be provided Mass flow Control Units (MCU’s) by electric, hydraulic or air motors. are required. NLR has developed In general, for a given available size, electric motors are cheap and very compact MCU’s that can be simple, but very limited in power. Usually, they are not powerful installed (if necessary) inside enough for propeller model applications and, in any case, require the fuselage of the model. With an additional water cooling system. these MCU’s the air motors can Hydraulic motors are also relatively cheap but, although better be controlled very accurately and than electric motors, they are quite bulky due to their limited energy independently of each other. content (power to volume ratio). Their relatively low price is offset Propeller blades with Kulite With the above smart model by the expensive hydraulic infrastructure they require (not normally dynamic pressure sensors components, NLR can supply all that is needed for powered propeller available at wind tunnels), they require very high supply pressures (>300 bars), and can be very contaminating in case of leakage. Also, testing. Since the interfaces between the various components is quite critical and can be quite complex, it is bridging the internal balance (see below) with recommended to charge only one party with these high pressures will affect the output of the integration of the complete (blades, hub, the balance significantly. rotating balance, telemetry) powerplant model. NLR supports the use of air motors for their Apart from designing and manufacturing significant operational advantages. They are (including calibration) of these components, relatively compact, light, clean and have the also the data gathering, registration and highest energy content of the three, but are analysis is an important issue. This is usually more expensive and require compressed air the responsibility of the customer, assisted by of up to 80 bars (normally available at most “Some 20 years ago, NLR made the wind tunnel, but also NLR can support wind tunnels). the decision to design and the customer in this with relevant advice. The air motor is usually supplied by the manufacture the propellers wind tunnel or the customer, and NLR does CONTACT for propeller-driven wind-tunnel Jan van Twisk, NLR the integration of the supplied air motor in the models from Carbon Fibre ... E-mail: email@example.com wind tunnel model, as well as the integration instead of metal” www.nlr.nl of its proprietary associated test equipment 124
WIND TUNNEL INTERNATIONAL | 2009
Subsonic Aerodynamic Testing Association 45th Annual Meeting held June 7-12, 2009 at Texas A&M
Subsonic Aerodynamic Testing Association The Subsonic Aerodynamic Testing Association (SATA) was formed in March 1965 to provide an organization for operators of low speed aerodynamic test facilities.
he broad objective of the organization is: “To provide at the operational level a means of interchange of ideas, techniques, and solutions of problems.” The general area of interest will include, but not be limited to:
aerodynamic facility equipment shall be discussions of a business nature. There is no ineligible for membership. limit on the maximum number of persons from any one member facility that may attend the d. Representation: Each member facility shall nominate someone as its official meetings; however, the normal number is two representative to this Association and representatives. The list of current members so inform the Chairman by letter. All can be found on the SATA website: http:// correspondence to the member facility shall www.sata.aero/ be addressed to this official representative. a. Design, performance, and economics of test facilities. SATA Membership Criteria b. Physical measurements, instrumentation, a. Membership shall be limited to How to become a and handling and reduction of data. aerodynamic facilities of sufficient member of SATA c. Facility operation and maintenance. size doing significant research and/or • You must be a low speed facility of development work. sufficient size to do significant research b. A provisional membership may be and/or development work. Meetings granted to a group planning aerodynamic • Send a letter of intent to Chairman Cor Regular meetings are held annually on a facilities of sufficient size to do, or Joosen at firstname.lastname@example.org rotating basis at one or more of the member engage in doing, significant research and • Give a presentation at a SATA conference. facilities. The host facility selects for each development work. Such membership meeting a program based upon the objectives shall not carry voting privileges and shall Current Officers described above. The program provides the be reviewed at the end of three years to • Chairman Cor Joosen (DNW) participants with a brief description and determine whether the membership • Vice-Chairman Alexander Broniewicz inspection of the host facility. should be extended to “full”, continued Each regular meeting includes a business (Volvo Cars) as “provisional”, or withdrawn. session for the purpose of elections (when • Secretary Victor Canacci (Jacobs/NASA Glenn) due), consideration of new admissions, c. Organizations primarily involved in the • Secretariat Jorge Martinez (Texas A&M commercial design and/or fabrication of selection of future hosts, and any other University). 2009 | WIND TUNNEL INTERNATIONAL
UNIVERSITY OF SOUTHAMPTON
Triple Olympic gold medallist Chris Hoy testing in the RJ Mitchell wind tunnel
WIND TUNNEL INTERNATIONAL | 2009
UNIVERSITY OF SOUTHAMPTON
Aerodynamic testing by athletes is mandatory for winning, particularly in power and speed sports like track cycling. Dr Kenji Takeda, Sciences at the University of Southampton, U.K. explains how his facility helped Team GB produce an unprecedented level of success at the 2008 Beijing Olympic Games as well as providing many similarly successful aerodynamic contributions to motor racing, yacht and powerboat design. Emirates Team New Zealand and Luna Rossa America’s Cup yachts, developed by WUMTIA engineers
eam GB’s performance in
Beijing’s Velodrome in August 2008 stunned the world as rider after rider won Gold Medals in the Olympic Games’ most impressive display of track cycling ever. Other nations were stunned as the British won medals in 80% of the track cycling events, including a dozen Gold Medals, and without dropping a single heat in the men’s sprint events. It is a victory that would have made Reginald Joseph Mitchell proud. For RJ was the designer of the Spitfire that was victorious over the skies of southern England during the last World War. It is in the wind tunnel bearing his name at the University of Southampton that Hoy, Kenny, Wiggins, Romero and other heroes at Beijing were able to hone their technique and equipment to take on the world once more.
Engineers from the Wolfson Unit for Marine Technology and Industrial Aerodynamics (WUMTIA) in the School of Engineering Sciences have worked closely with UK Sport to elevate the development of track bikes and riders to the level of the America’s Cup and Formula One. By using their extensive knowledge, skill and intuition, they have focussed on areas in which performance gains of tenths of a second can make the difference between a medal and nothing. Track cycling is all about power and speed. About 80-90% of a cyclist’s effort is used to overcome air resistance, hence the importance of wind tunnel testing. Subtleties such as rider position, helmet design, and even the suits they wear, can be optimised to reduce aerodynamic drag, allowing the cyclists to go faster. Wolfson Unit engineer Dr. Martyn Prince, who worked with British cyclists in the Southampton wind tunnel, said: “We congratulate the British Cycling team on this amazing achievement. It is great to be able to apply our engineering expertise in this way and a privilege to work with these top athletes. 2009 | WIND TUNNEL INTERNATIONAL
UNIVERSITY OF SOUTHAMPTON
Student race car project in the RJ Mitchell wind tunnel
“We’re delighted that we have been able to help them achieve Gold in Beijing, making all of our hard work together worthwhile.” The Wolfson Unit is one of eight organisations chosen as Innovation Partners to UK Sport, providing support to the UK’s best athletes and coaches so that they can reach their full potential in the Olympics and other international competitions. Head of Research and Innovation at UK Sport, Dr. Scott Drawer, added: “Working with the team at WUMTIA has been a truly world-class experience. Their enthusiasm and passion for excellence has never faltered during this Olympiad. “We hope our working relationship will continue to go from strength to strength over the next four years as we try and build on the knowledge and insights we have gained in cycling and many of our other leading sports.” In addition to supporting British Cycling, the School of Engineering Sciences currently has three Engineering Doctorate students sponsored by UK Sport to allow in-depth study of other sports in a research-based environment. 128
Southampton’s wind tunnels have an illustrious history, having been used by most of the current Formula One teams. Many teams have used both of our large, low-speed tunnels for their car development work since the 1980s, and continue to collaborate with the School of Engineering Sciences for research and teaching. Superstars, such as Adrian Newey, Formula One’s most successful car designer, cut their teeth in the wind tunnels at Southampton, both as students and afterwards working for racing teams. Most recently, the Ferrari A1GP race car has been developed in the RJ Mitchell wind tunnel and is now being used in the World Cup of Motorsport from China and Malaysia, to Mexico and South Africa. Wolfson Unit engineers use the tunnels extensively for marine work, including work on the Luna Rossa and Team New Zealand America’s Cup yacht race contenders as part of the R&D teams. The University is a centre for aircraft noise research, incorporating technology centres for Airbus and Rolls-Royce, with wind tunnels used for aeroacoustic studies using state-ofthe-art microphone array technology. Southampton graduates are prized by companies involved in high performance engineering. As one of the few universities in the world with such an extensive wind tunnel complex, we are able to give students a unique learning experience using industry-leading experimental facilities. Student projects have included developing the Bonneville 400 world F1 land speed record car with BAR Honda F1, and the Quicksilver world water speed
“Superstars, such as Adrian Newey, Formula One’s most successful car designer, cut their teeth in the wind tunnels at Southampton, both as students and afterwards working for racing teams” record contender. We probably supply more aerodynamicists to the Formula One industry than any other university in the world, with many Ship Science graduates going onto racing yacht and powerboat design. The University of Southampton is unique in combining academic excellence in aerodynamics, performance-focussed consultancy expertise and an exciting environment for teaching and research. As long as the big fans keep turning, Southampton will continue to help keep teams on the podium, whether it’s in the Olympics, Formula One or the America’s Cup, and supply the world with engineers of the highest calibre. CONTACT Dr Kenji Takeda, University of Southampton E-mail: email@example.com www.windtunnel.soton.ac.uk WIND TUNNEL INTERNATIONAL | 2009
HORIBA Wind Tunnel Balance with Turntable and Moving Ground System
HORIBA Wind Tunnel Balance System for Vehicle Aerodynamic Development Vehicle development steps and optimization of aerodynamic properties are often carried out in wind tunnel facilities. Even though many investigations can be done with numerical methods, realistic tests with true air flow simulation around the vehicle remain indispensable. The demand for new modern wind tunnels with the capability of air flow simulation (especially at the underside of the vehicle) combined with a high accuracy of force measurement is growing worldwide. The HORIBA Wind Tunnel Balance System together with its integrated moving ground system fulfils both re-quirements exactly. By Dr. Hans Vogt of HORIBA Europe GmbH
he improvement of vehicle aerodynamics is an can be equipped with a important step to optimize fuel con-sumption, driving moving ground system (also comfort, performance and acoustics. A common factor called ‘5-Belt-System’) which to describe the quality of the aerodynamics is the drag makes the air flow at the coefficient Cd, which can be measured in a wind tunnel underside and around the (together with other aerodynamic coefficients) using a wind tunnel wheels much more realistic. Co-ordinate System showing three bal-ance. The vehicle is placed upon the measuring platform of This moving ground system Vehicle forces and moments measured with the Wind the balance. The wind tunnel balance now allows the precise is build up of a central Tunnel Balance determination of six forces and moments in-duced by the air flow. moving belt unit (also called ‘Rolling Road System’) which is running In a classical wind tunnel the air flow at the underside of the vehicle at wind speed between the wheels and of four wheel spinning units is not completely realistic, because a boundary layer exists close to which are rotating the wheels with wind speed. In this case the four the test section floor. Conse-quently, in modern wind tunnels special wheel spinning units are also part of the force measuring system of methods and equipment are used to improve air flow simulation at the balance. Us-ing these systems, vehicle speeds of up to 250 km/h the underside of the vehicle. The HORIBA Wind Tunnel Balance can be achieved. 2009 | WIND TUNNEL INTERNATIONAL
Scale Wind Tunnel Balance in commission at the factory– AERO COMP 2000
Even small force components in the order of 100 gm. can be measured while a static preload (caused by the mass of the balance platform, wheel spinners and vehicle) of approx. 15 tons ... is applied force components in the order of 1 N (100 gram) can be measured while a static preload (caused by the mass of the The turntable and the lift units. The lift units are integrated balance platform, wheel spinners and vehicle) of approx. around the wheel spinner units. 150000 N (15 tons) in vertical-force direction is applied. By using high quality load cells and a precise high-resolution digital Wind Tunnel Balance The HORIBA Wind Tunnel Balance is a external, platform-type balance. amplifier system, the high-est measurement accuracies in the order A rigid, massive platform is held statically fixed at six points. These of 0.02 % to 0.05% of full measuring range can be achieved. The six points are connected (three in horizontal direction, three in vertical measuring range of vertical force is up to 25000 N. Additionally the direction) to a frame with flexible con-nection rods. At the end of each cross interference of different force components is eliminated by rod a force sensor (Load Cell) is integrated. A com-puter program is special calibra-tion and data evaluation methods. The HORIBA Wind Tunnel Balance system can also be used for used to calculate the forces Fx (Longitudinal-Force), Fy (Lateral-Force), Fz (Vertical-Force) and the three moments Mx (Roll-Moment), My other test objects such as aircraft models, ship models, motor bikes (Pitch-Moment), Mz (Yaw-Moment) from the six force sensor signals. and others. HORIBA Balances are delivered in three standard sizes for testing This ‘computer-separation’ method is to be distinguished from other of models or in any size according to customers’ requirements for balance types using mechanical separation methods. The advantages of the HORIBA balance system are that its full scale vehicles. All functions of the balance system can easily be remote controlled construction is very robust and simple, it is stable in the long term and is maintenance-free. No lever systems and no hydraulics are from a host com-puter with an Ethernet TCP/IP link. Additionally a used. Also, no tare compensation system is necessary. Even small stand-alone operation program is available. 130
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system can be placed in front of the center belt unit. The polymer belt of the center belt unit is driven by two servo drives with a maximum electric power of 250 kW. The lateral belt position is detected with an optical laser position sensor. Belt lateral position and belt tension is controlled and adjusted fully automatically with a tracking station which is driven by two servo drives. To prevent the belt from lifting off due to aerodynamically induced low pressure be-low the vehicle the frame of the center belt unit is equipped with pneumatic suction chambers to create a low pressure under the belt. HORIBA Wind Tunnel Balance with Turntable and Moving Ground System As a special alternative to the 6-component balance with 5-belt ground-simulation, HORIBA also offers Turntable and Vehicle Lift System 7-component balance, featuring a separate To rotate the vehicle around the vertical z-axis the Wind measuring unit for each wheel of the test Tunnel Balance and the test section floor can be rotated. vehicle, combined with a dedicated boundary A vehicle lift unit is integrated in the Balance system to layer suction system. lift the vehicle up to 1800 mm allowing fast modification HORIBA Wind Tunnel Balance systems work in the wind tunnel at the underside of the vehicle. have a proven track record for reliability and measurement accuracy unparalleled by any Moving Ground System Wheel Rotation with Wheel Spinner other supplier of such equipment in the world. The Moving Ground System consists of the center belt The HORIBA Wind Tunnel Balance System is the first choice for system and four wheel spinning units. The center belt unit is integrated modern automotive wind tunnel facilities where simulation quality, into the Turntable without contact to the balance platform. The wheels of the vehicle are standing on the four wheel spinner belts measurement accuracy, robustness and easy handling of the system which are mounted on the platform. The aerodynamic forces of the are required. vehicle are thus transmitted to the platform via the wheel spinners and CONTACT the rocker panel restraint system, which holds the vehicle in position. Dr. Hans Vogt, HORIBA Europe GmbH Additionally to the moving ground system a boundary-layer suction E-mail Hans.Vogt@horiba.com
HORIBA Wind Tunnel Balance systems have a proven track record for reliability and measurement accuracy
Finding the Right Balance
HORIBA Wind Tunnel Balance Systems are the first choice for modern automotive Wind Tunnel facilities where simulation quality, measurement accuracy, robustness and easy handling of the system are required. From model scale to full size seven component systems, HORIBA has the right balance
From Model Balances to Full Scale Systems
HORIBA WTI 0809.indd 1
2009 | WIND TUNNEL INTERNATIONAL
Modular design guarantees adaptability and extensibility In the context of automotive development, modern wind tunnel technology constitutes an essential element for Audi AG to further optimize their vehicles. In this respect, the wind-tunnel centre in Ingolstadt with its three wind tunnels provides Audi engineers with unique test facilities. As in the already existing aeroacoustic wind tunnel, a comprehensive wind-tunnel control system from Werum Software & Systems and S.E.A. Datentechnik is at the heart of the new climatic wind tunnel, ensuring trouble-free operation. By Ulf Kuehnle, Project Manager, Werum Software & Systems AG and Jรถrg Hessdorfer, head of software development, S.E.A. Datentechnik GmbH 132
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arly in 2008, Audi commissioned its new climatic wind aerodynamic tests on models and real vehicles tunnel in Ingolstadt, Germany. The installation permits • A thermo wind tunnel to test the cooling of combustion engines, the realistic simulation of a vehicle being driven on gearboxes and brakes the road even under the most extreme environmental • A new climatic wind tunnel for such tests as windshield deconditions. The wind tunnel is designed for passenger icing, coolant-performance measurement at high temperatures, cars and SUVs, as well as for sports and racing cars. and heater operation at low temperatures. This means that Audi now has a wind-tunnel centre with When the new facility was built, Audi also took the opportunity to three sectors: completely modernise the wind-tunnel control system. As a result, • An aeroacoustic wind tunnel to carry out aeroacoustic and the new wind tunnel is equipped with a control system based upon 2009 | WIND TUNNEL INTERNATIONAL
The operator console (left) and in the background of it the user workstation Source: Audi
Component structure of the wind-tunnel control system WTCS with five levels Source: Werum/SEA
the WTCS (Wind Tunnel Control System) from Werum and S.E.A. As early as 2003, these two specialists for large-scale test-stand software planned and installed a WTCS control system for Audi’s aerodynamic and aeroacoustic wind tunnel. In the meantime, both control systems — which basically have the same layout — have more than proved themselves in practice.
WTCS control system architecture Werum/SEA’s WTCS control system platform is based upon precisely defined, self-contained functional components. It is comprised of configurable core components and application-specific modules. The modular system is supported throughout by a client-server architecture which, for instance, enables any number of operating and display workstations to be set up. Each and every subsystem or measuring 134
system is connected and triggered individually and independently. Such essential functional components as the configuration and data-management, or the control of the test sequences, are standard Werum modules. The interfaces to the various subsystems and functions are designed so that the connection of standard tools is a simple matter. Further-ranging project-specific control-system functions and procedures were implemented by Werum in line with Audi specifications and in close cooperation with operators and users. Depending upon requirements and architecture, the overall system can be distributed among several computers. Each functional component is allocated by configuration to a specific computer. The hardware is based on standard PC systems using Windows and Linux operating systems. The wind-tunnel control systems can be operated fully autonomously. The data server for the central processes and databases is, at the same time the interface to the Audi data network. The configuration management and the data management are available for all component levels. The configuration management covers all data for the parameterization of the control-station functions and the coordinated operation (including, among other things, set-up definitions and sequence charts). The wind tunnel’s quality-assurance measures are based on these data. The data management administers the measurement data, links these with the corresponding test configurations, and transfers them to the archive so that they are also at the disposal of the Audi engineers during tests at a later date. WIND TUNNEL INTERNATIONAL | 2009
Audi and Werum/ SEA concentrated on an uncomplicated operating interface which the operator can intuitively understand and control Reliability is trumps: High-level data integrity thanks to hardware redundancy Source: Werum/SEA
selection of the most important process parameters such as wind velocity, humidity, and air temperature. After all, in addition to already predefined displays and presentations, the user can also work in the WTCS with individually The control system in practice At present, the WTCS users have more than 50 different dialogs and designed display elements. The layout of the display interface was displays available for operation of the wind tunnel. The control system developed by the Audi wind-tunnel specialists in cooperation with differentiates between the users according to their roles: Operator, Werum/SEA. Technically speaking, the control system’s display and Administrator, Test Engineer, Measurement Engineer and User. operating interface (visualisation) is independent of the system’s actual Depending upon his/her particular role, the person in question is operating procedures (e.g. data management, limit monitoring, event management). This means that the dialogs can already be tested before allocated the corresponding authorizations. This means that the wind-tunnel operator has access to all control they are actually taken into operation in the wind tunnel. Thanks to the sequence control, the person operating the test bench options on all installations and is presented with all wind-tunnel data is able to automatically run through test sequences which have and measurement values. A user on the other hand, is allocated a separate workstation where been completely configured beforehand. This contributes towards the measurement data “only” are displayed visually. The user can in minimising faulty entries and sources of error. Formerly, the operator no way intervene in system operation. In order that he/she can work was forced to adjust many of the parameters by hand whilst the actual with the measurement data without delay, these are automatically test run was taking place. Today, he or she simply calls up the already imported into a table, along with the evaluations, and placed at the prepared test configurations from a database, or adjusts other tests to the current requirements. This rich stock of configurations also user’s disposal together with the test records. guarantees a high Compared with level of reusability the previous control for already existing system, the windtest configurations tunnel operator is and permits the direct now provided with comparison between considerably more identical wind-tunnel information from tests performed on the wind-tunnel different dates. A tests. For this reason, further advantage of Audi and Werum/ the uniform control SEA concentrated system lies in the on an uncomplicated fact that the measured operating interface values for a given test which the operator are consistently timecan intuitively synchronous. understand and For Audi, the short control. The cockpit setting-up times for is the central display Source: Audi new test scenarios and presents the result in increased m o s t i m p o r t a n t The most important wind-tunnel parameters shown graphically wind-tunnel parameters in a clearly arranged way. A status display efficiency. Not least thanks to the test database and the clearly defined indicates in colour the operating status of each subsystem, and, in data management, this control system ensures a no-delay test start and a case of deviations from set point values, immediately turns to red. trouble-free test run. Compared to the former thermo wind tunnel, almost This means that since the operator is warned visually in the event of four times as many tests can be performed in a given period. deviations, he/she is no longer forced to directly monitor the process CONTACT Carsten Stein, Werum Software & Systems parameters. Furthermore, upon demand, the cockpit displays online a E-mail: firstname.lastname@example.org 2009 | WIND TUNNEL INTERNATIONAL
Nimrod Model in the 4.0m Low Speed Wind Tunnel
The BAE systems wind tunnel department consists of 6 major facilities and is capable of a diverse range of testing capabilities, ranging from hover up to Mach 6. Brian Cleator, BAE reports
AE Systems Wind Tunnels have contributed to the research in 1962/63 and the transfer of the Vickers Armstrong 13’ x aerodynamic development of all of the company’s 9’ wind tunnel from Weybridge in 1992. These facilities today make manufactured aircraft since the Canberra bomber, Warton one of the most advanced research facilities in the world.
including Harrier, Tornado, Typhoon, JSF and, more recently, UAVs. BAE Systems also carry out work for 4.0m Low-speed Wind Tunnel. several external customers. The 4.0m Low Speed Wind Tunnel is a closed return tunnel with a
Specialist activities include model Design and Manufacture, Low maximum test speed of 105 m/s. The working section is nominally 4m Speed testing, High Speed testing, Ground Erosion studies, Hot Gas wide x 2.7m high x 7.3m long. Flow conditioning and a large 10.6:1 contraction ratio combine to give excellent flow quality. Ingestion and high-temperature nozzle flow investigation. Models can either be sting-mounted on an internal strain gauge balance or strut-mounted on the under-floor virtual centre History In 1954 the expansion of Warton’s research and development facilities mechanical balance. was initiated. The first tunnel to be constructed was an 18” x 18” wind tunnel which was commissioned on the south side of the Warton base, 5.5m Low-speed Wind Tunnel powered by two Rolls Royce Nene jet engines. Two high speed wind The 5.5m Low speed Wind Tunnel was designed specifically for the tunnels were built during the period 1956-60. One tunnel had a four investigation of powered lift configurations, but because of the large test foot working section able to test aircraft at speeds up to Mach 3.7 and section it has since proved to be eminently suitable for high incidence a companion 18” section for guided weapons research at speeds up and rotary derivative testing. Models are typically sting-mounted on to Mach 6. These facilities were supplemented with the construction an internal strain gauge balance. In recent times the tunnel has been of a wind tunnel for Short Take Off and Vertical Landing (STOVL) extensively used to develop STOVL configurations 136
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Typhoon Model with live stores in the 1.2m High Speed Wind Tunnel
1.2m High-speed Wind Tunnel This is an intermittent trisonic blowdown type, operating from a storage pressure of 4,200 kPa and exhausting to atmosphere. The tunnel is capable of variable Reynolds number testing over a Mach number range 0.4 to 3.7. The tunnel has been utilised extensively to support Typhoon development, including specialised intake, afterbody and “live store” testing. The facility also has the capability to simultaneously pitch and roll missile models, delivering high levels of productivity.
Guided Weapons Wind Tunnel with High-speed Blower Facility The 0.45m Guided Weapons Wind Tunnel is a blow-down type, operating from a storage pressure of 4,200 kPa and exhausting to atmosphere. The tunnel provides variable Reynolds number testing over a Mach number range 1.7 to 6.0. Models are mounted on a model cart that simultaneously pitches and rolls the model whilst measuring loads on an internal strain gauge balance. This delivers productivity that is comparable to a continuous running facility. The tunnel also drives a High Speed Blower facility (HSBF). The HSBF provides an open test environment up to Mach 1.8 in various nozzle configurations up to 1m in diameter. The blower has good axial and cross axis visibility and can be used for store ejection / deployment, flare firing, pilot equipment air blast testing, parachute deployment tests and general load and pressure measurement studies. 2009 | WIND TUNNEL INTERNATIONAL
“Our wind tunnels have contributed to the aerodynamic development of … Canberra, Harrier, Tornado, Typhoon, JSF and UAVs” Hot Gas Laboratory The Hot Gas Laboratory (HGL) tests large scale models at full scale pressures and temperatures. It is used primarily for Ground Erosion characterisation studies and also for structural, environmental and infra-red signature testing. The HGL contains a heavily modified combustion chamber mounted on a support frame allowing exhaust gas temperatures up to 1100C at pressures of up to 5 atmospheres.
Advanced gas facility The Advanced Gas Facility consists of the Ground Effects Rig (GER) and the Reaction Control System (RCS) cell. The GER is designed to investigate ground effect jet flows on STOVL configurations. These include the evaluation of hot gas ingestion and jet-induced loads. The RCS development cell has been utilised in the development and qualification of the Harrier reaction control system. The facility is able to provide high temperature and pressure gas flows to a variety of nozzle and valve configurations. For more information Visit: http://www.baesystems.com/ ProductsServices/bae_prod_mas_wind_tunnel CONTACT Brian Cleator E-mail: email@example.com 137
End of the Tunnel Built as part of the construction projects designed to offset the effects of the Great Depression and, for more than seven decades, site of some of the most significant aviation developments in history, the Langley full-scale wind tunnel may soon blow for the last time. Designed to test full-scale aircraft, it tested many of the bombers and fighter planes used in World War II. Although it was retired in October 1995, it is one of NASA’s largest wind tunnels and is a National Historic Landmark.
View of the 30 x 60 Full Scale Tunnel’s huge (434 by 222 feet, and 90 feet high) exterior from the Little Back River in October 1930
In supreme irony, the last plane to experience its giant fans – the Boeing X-48C (see News, page 9) – may presage future aviation. But by the time you read this the wrecking crews may have already moved in as NASA focuses more resources on space vehicles. The full-size tunnel – known internally as the 30x60 tunnel – sits on Langley Air Force Base, near Hampton, Va. on the shores of the Chesapeake Bay. As homage to this wonderful old lady, here are some highlights of its 78 years…
Construction in 1930
Wing test 1932
Vought SU-2 Corsair naval scout aircraft, testing in 1934. The enclosure around the engine is not the Langley-developed NACA cowling, but the less efficient Townend ring cowling
Not all flying devices were heavier than air. Here, in 1935, a 1/40th scale model of the airship USS Akron undergoes tests
Lockheed YP-38 Lightning, December 1941
Mercury full-scale capsule model, 1959. Much of the research and development of the Mercury program was conducted at Langley
AST model, 1975. Designed to fly in 2010, the AST was envisioned to fly 300 passengers across the Pacific in about four hours at Mach 2.4 (approximately 1,600 mi/h or 1950 km/h) for a modest increase over business class fares
Air2Tunnel Europe..................................................................................................................................70 AOS Technologies ..................................................................................................................................89 BAE Systems............................................................................................................................................65 BIHRLE Applied Research Inc..........................................................................................................63 Bustec..........................................................................................................................................................93 Darchem Engineering.......................................................................................................................... 27 Dynamotive / ReACT Technologies..............................................................................................29 ELD Engineering Laboratory Design.............................................................................................61 HBM.................................................................................................................................................................. 7 Horiba Automotive Test Systems................................................................................................131 Jacobs Technology Inc..................................................................................... Outside Back Cover LaVision Gmbh .......................................................................................................................................85 Maha-AIP GmbH & Co. KG..................................................................................................................71 Microflown Technologies....................................................................................................................75 138
15 percent model of Lockheed F-18E, 1995
MTS Systems Corporation ........................................................................ Inside Front Cover NLR................................................................................................................................................................... 4 Pacific Instruments, Inc..................................................................................................................... 111 Patersonlabs Inc ................................................................................................................................ 103 PCO-AG.........................................................................................................................................................59 Pratt & Miller Engineering................................................................................................................. 97 RUAG Aerospace ..................................................................................................................................28 SBI................................................................................................................................................................... 91 The Cooke Corporation.........................................................................................................................81 Tri Models, Inc ....................................................................................................................................... 117 University of Southampton ..............................................................................................................99 VZLU-Aeronautical Research and Test Institute.................................................................109 WBI................................................................................................................................................................ 91 Werum Software & Systems / S.E.A Datentechnik........................................................105 Windshear ................................................................................................................................................43 WIND TUNNEL INTERNATIONAL | 2009
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Published on Oct 14, 2009