5 - Propulsion, Environmental Impact, Noise and their influences on each other

AIAA Team Aircraft Design Competition 2009-2010

Introductory Lectures on Aerospace Design Nov. 13th, 2009

University of Southern California

Sina Golshany

Lecture-5 Propulsion, Noise, and Environmental Impact

Principals of Propulsion Systems

Roles of Propulsion Systems – Primarily Role: – Producing thrust force by consuming fuel (via ejecting high speed air)

– Secondary Role: – Provide Electric, Hydraulic, and Pneumatic power for systems, as well as compressed air for pressurization and ventilation systems.

Classification of Propulsion Systems - Piston Engines: -

Moderate to low specific fuel consumption Low speed & relatively low altitudes High Noise Low power/weigh ratio More moving parts per unit weight Constant need for cooling Cheep per unit weight (or power) Limited in terms of max. power attainable

Main Jet Engine Performance Parameters -Engine Installed Thrust : thrust force excreted by the engine, after the extraction of power by generator, hydraulic pumps, etc‌ -Engine Installed SFC (Specific Fuel Consumption): Fuel consumed per unit thrust force generated per hour. Most determining factor in selecting two equal engines. Engine optimization revolves around cutting the SFC.

-Installed and Uninstalled values for engine performance parameters are significantly different.

Engine Performance Representation

-Carpet Plots to represent complete engine performance in form of an “engine map�:

Mach #

Altitude

Classification of Propulsion Systems - Turbine Jet Engines: - Use the momentum of expanding, and accelerating jet of hot air to create thrust force.

- Combinations of rotor-stator pairs, large fans, turbines and combustors are used to materialize this.

- They may or may not have by-pass air flows.

- Process: 1-Suction 2-Compression 3Ignition 4-Expanssion/Jet acceleration 5Torque Extraction

Classification of Turbine Jet Engines - Turbojet Engines: -

High specific fuel consumption More efficient for high speed & very high altitudes Not efficient for Transonic flight High Noise levels Lower thrust/weigh ratio than turbofans Lighter, smaller, less drag, easier to integrate (except for the length) - Cooling is an issue, reliability is less than other types discussed.

- Mostly Obsolete

Classification of Turbine Jet Engines - Turbofan Engines: -

Concept of By-Pass Ratio Low fuel consumption More efficient for Transonic speed & moderate altitudes Not efficient for Supersonic flight (unless with low BPR) High Noise levels(Fan noise is added) Heavier, larger, more drag, harder to integrate Excellent cooling due to the bypass air, very reliable Most common configuration for both military and commercial designs

Main Turbomachinery Components - Fan: - High advance ratio blades, moving large quantities of air in a relatively slow speed.

- Compressors: - Typically Axial compressors, consisting of rotor and stator stages (in pairs).

- Turbines: - Typically Axial turbines, extracting a small fraction of mechanical energy from the fast moving hot exhaust air flow.

Operation of axial jet engines - Process of a typical Turbofan engine:

Stages of a Turbofan engine

Classification & Envelopes of Operation

-Each Type of Engine is Optimum for a particular Mach #/Altitude Combination

Modern Concepts: Geared Turbofan

-Geared Turbofans utilizing Epicyclical gears

– Lower fan RPM – High core RPM – Lighter fan blades – Far less noise, Higher BPR – Double digit reductions in SFC – Up to 50% reduction in CO2 levels – Even better for NOx levels

Modern Concepts: Geared Turbofan

- Not a completely novel idea! (1978 Garrett)

Modern Concepts: three-Spool Turbofan

-Three-Spool Turbofans utilizing three co-axial shafts

– Optimum fan RPM – Optimum LP & HP RPM – Composite fan blades – Noisier than P&W-1000, Similar (or lower) BPR – Double digit reductions in SFC, lower than P&W-1000 – Up to 50% reduction in CO2 levels – Even better for NOx levels

Modern Concepts: Open Fan Engines

– Very High BPR (>24) – Lowest Attainable SFC – Lowest Emissions – Very Noisy (both near-filed and far-field noise) – Could be both pusher and puller – Due to large diameter and heavy weight can have serious integration issues.

Integration of Open Fan Engines

Main Considerations: -

Far Field Noise Near Field Vibration Ground Clearance Safety

Ducted Open Fan Concepts

o Reduce Far Field Noise: - Seams Very Promising - Utilization depends on the availability of propfans before 2020.

Most likely aft fuselage installation due to fan diameter

Engine Performance Interdependency -Altitude Effects: -As altitude↑ thrust ↓, proportional to air density -As altitude↑, SFC↑, inversely proportional to temperature and directly proportional to drop in air density (i.e thrust component of the SFC) -Mach Effects: - As Mach number ↑, SFC ↑ (Less efficient turbomachinery and intake system in higher speeds) - As Mach number ↑, thrust ↓ (ditto) -Intake pressure recovery: - As pressure recovery ↑, SFC ↓ - As pressure recovery ↑, thrust ↓

Engine related Trade Studies: – Should be done separately for each configuration.

– Should be done separately for each fuel type – A wide range of BPR must be considered (i.e. from 5-55) – – –

Environmental Impacts

Pollutants:

– Gassy elements: – CO, CO2 – Nox – SO,SO2 – Vapor (Low Alt.)

– Solidified Elements – Carbon Particles – Ice (High Alt.)

– – –

Prevailing Methods of Quantification - Very hard to model emissions theoretically.

- Imperial methods are used.

- For NOx emission level, NOx severity index is used:

- P3 and T3 : pressure & temperature inside the combustion chamber - war : Mass Ratio of liquid water to air entering the combustion chamber.

Prevailing Methods of Quantification - Similar methods exist for Carbon Oxides - Each environmental parameter can be integrated with an engine map:

Aircraft Noise: Goals, Methods and Principals

Basics of Lift & Drag Generation:

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Created by any aerodynamic shape that is capable of creating a pressure difference on it’s upper and lower

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sides.

Pressure difference is usually achieved by causing a difference in flow speed.

Drag is a consequence of both production of lift and molecular friction with “wetted” surfaces.

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Airfoil shaped geometries try to maximize lift and minimize drag.

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Flow Feature Dependencies: General Flow features depend on: - 1-Flow Regime (Mach Effects) 0-0.7: Subsonic (almost no Mach effects) 0.7-0.95: Transonic (benign Mach effects) 0.95-2: Super Sonic (significant Mach effects) 2-7: Hyper Sonic (dominated by Mach effects)

- 2-Reynolds Number (i.e. turbulence level):

Ď Vl Re = Âľ

- 3-Angle of Attack - 4-Significantly influenced by geometry in contact with the flow.

Turbulent vs. Laminar Flow: - A major complication in the process.

- Turbulence is still an open question.

- Experimental Aspects - Empirical Methods - Numerical Models for turbulence - Using complex mathematics, PDEs & Chaos Statistical techniques + Experiments - Turbulence+Mach effects

Aerodynamics Methods of Analysis

Experimental Aerodynamics: – – – –

Earliest method of approach If performed right possibly the most reliable Time consuming and very expensive Corrections have to be applied

– – –

Computational Aerodynamics: – –

Computers have drastically changed the approaches to aerodynamic analysis, but still have to be used with great deal of caution.

Still, they are a great solution for design problems.

– – –

Computational Aerodynamics: – –

Lattice Based Models (like AVL) are simpler to use & take shorter times to converge Lowe accuracy but more flexible

– – –

Fuselage Aerodynamics: Performed Trade Studies & Selected Design Strategy

Optimization of Fuselage Geometry: –

The goal is to increase the Drag Divergent Mach number MD:

–

This is mainly a function of Length to diameter ratio (L/d) of the nose and aftbody geometry:

Optimization of LN/d to delay Drag-Rise: For The nose segment, per ESDU 74013 Max Cruise Speed is required to be 0.83

0.83

1.25 Âą0.15

Optimization of LA/d to delay Drag-Rise: For The aft-body segment, per ESDU 74013 - Max Cruise Speed is required to be 0.83 - The aft body fineness ratio is considerably less than 1.

- The aft body is NOT a limiting factor for Drag rise Mach number.

0.83

<<1 Âą?

Optimization of Nose Section Geometry : - Fuselage Wave & pressure Drag impacts on nose geometry: - Experimental results have shown a correlation b/w blunting ratio of the nose geometry b=(2r/D) and the wave drag and pressure of the fuselage.

Optimization of Nose Section Geometry : - Minimizing the wave drag using ESDU item 83017 - The average radius of curvature ratio becomes important - The average radius of curvature of the nose compartment :

- Note that it is highly curved in the front and slightly flat at the region of installation of the cockpit windows.

Optimization of Nose Section Geometry : - Minimizing the wave drag using ESDU item 83017 average radii of curvature ratio of 0.7 -

d/D=0.6

Optimization of Nose Section Geometry : - Minimizing the wave drag using ESDU item 83017 average radii of curvature ratio of 0.4 -

d/D=0.7

Optimization of Nose Section Geometry : - Minimizing the Pressure drag using ESDU item 89033 for AOA of 0 degrees:

B=6.6

B=6.2 B=5.8

M=0.83

Optimization of Nose Section Geometry : - Minimizing the Pressure drag using ESDU item 89033 for AOA of 5 degrees:

B=0.2

M=0.83

A Case-Study of CFD Application: - CFD tools could be used to streamline the fuselage geometry to improve flow field issues.

Aerodynamics of Lifting Surfaces: Elements, Principals & Design Strategy for Low-Speed & High-Speed Aero

Airfoil Characteristics: Lift Producing Cross-Sections

Lifting Surfaces or Bodies: - General Characteristics: - Pressure differentials exist b/w top and bottom sides.

- Velocity variations exist b/w top and bottom sides.

- Bernoulli's Principal is an analogy to what takes place on an airfoil shaped surface: v2 P 2

+

Ď

= Constant

-

Airfoil Categorization & Sources:

By Designer, Type, or Geometry.

Different types are optimized for different flow regimes: - Thick Airfoils (t/c: 13-17 %) optimized for slow speeds.

- Transonic Airfoils (t/c: 7-12 %) optimized for Transonic flight.

- Thin Airfoils (t/c: 3-7 %) optimized for supersonic & transonic flights.

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Among Transonic Airfoils:

- Super Critical Airfoils

- Natural Laminar Flow Airfoils - Supercritical Airfoils with Diverted Trailing Edge

Flow Features for Transonic Airfoils: - Flow around Transonic, Super Critical airfoils

RAE-2512

RAE-2822

SC-20712

Airfoil Aerodynamic Properties: - NACA Charts to describe airfoil performance

Flow Features for Transonic Airfoils: - Flow around, Non-Super Critical airfoils - Formation of Shock is visible - Analysis is done at very low Re # (Notice the transition)

SC-20714

Low-Speed Aerodynamics: High Lift Devices Purpose, Sizing & Analysis

Principal of High-Lift Devices: -

They divert the wingâ&#x20AC;&#x2122;s local flow downwards, At the same time they improve the pressure differential b/w top and bottom surfaces near the trailing edge of the wing Dominantly functional in low Re #s Dominantly incompressible flows No Mach effects Transition occurs towards the TE Overall: In some aspects analysis are simple: - No Mach effects, more laminar flow

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Overall: In some aspects analysis are more complex: Unsteady features, High AOA, High flow path deflections.

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Wing Geometry, TE devices:

Main Types of TE High-Lift Devices: -

Split Flaps:

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Simple Construction Light Weight Simple Analysis

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Single Slotted Flaps:

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More lift Heavier & more noise Harder to optimize

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Double Slotted Flaps ditto -

Flow Features of High-Lift Devices:

unction 1: Diverting the TE flow ownwards unction 2: Amplifying the rear pressure ifference via a high speed “jet” at the rifice. ●

Flow Features of High-Lift Devices: Point of Transition

lotted flaps are more powerful per unit area lotted flaps are more aerodynamically efficient per nit weight They are more complicated to design & build

Wing Geometry, LE devices:

Main Types of LE High-Lift Devices: -

Simple Slat:

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Powerful Heavy & Noisy Complicated deployment

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Upper Surface Kr端ger:

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Less Powerful Lighter & Less Noisy Simple Deployment

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Drooped LE Device Obsolete Ultra Complicated -

Combinations & Lift Generation: - Combinations of High lift devices are compared schematically:

Sizing of TE devices:

–

-Three main parameters to solve for:

–

1- flap chord to wing chord ratio

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2- Outer span-wise location of the flaps

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3- Deflection Angles

–

They all Depend on each other. One has to be picked to start with. ●

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The flap chord to wing chord ratio is often selected to be 0.30 in commercial aviation design.

We will use a single slotted flap for this example.

Optimization of TE devices: â&#x2014;?

Based on ESDU Item 93019:

Max. CL

45-50 deg.

Low-Speed Flow Visualization:

High-Speed Aerodynamics: Transonic Wing Design Elements

Mission Influences on Aerodynamics:

Weight during the cruise determines the required lift coefficient (and consequently Drag coefficient) CL has to be chosen respectivly â&#x2014;?

CL to Max. E Cruise CL to

Min. Fuel Burn

Process of Preliminary Wing Design:

ESDU 97017 Process: ● 1-Select a Primary DP ● 2-Select an airfoil ● 3-Perform Analysis ● 4-Perform Optimization ● 5-Repeat till Satisfied ● 6-If necessary change airfoils, twist ,etc… ●

Flow Field Around a wing:

Sweep Effects Reducing the critical Mach number Consequently causing an In-wash flow on the top side Presence of wing causes an up-wash in front and a down â&#x2014;? wash behind the wing in the flow field. â&#x2014;?

Flow Field at Wingtips:

weep Effects In-wash (upper) & outwashes (lower) combination causes vortex at the wing-tips (+ P differential) his is a large source of waste of kinetic energy in form ● of vortex drag (AKA induced drag) ●

Flow Field at the Wingtip:

Winglets to Improve the Aero Efficiency:

Different geometries can be used Multi disciplinary optimization for: - Wing Oswaldâ&#x20AC;&#x2122;s Efficiency - Wing Weight s. AR and Taper ratio of the wing â&#x2014;?

Winglets to Improve the Aero Efficiency:

- To isolate the upper side flow fields from the lower side flow field. ● - Different geometry types for different Methodologies: Cant Angle could be optimized. ● Their AR and Taper ratio could be optimized.

AVL could be used Trade studies are often performed n form of ● non-dimensional efficiency factors. ●

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Winglets Optimization: â&#x2014;?

- Vortex Drag Parameter Ratio (V-Drag to minimum theoretical possible value) vs. Flutter Measure of Merit.

High-Speed Surface Flow Visualization:

urbulent Transition on ● ● Leading edge for Airbus A-340 ●

urbulent Transition on ● Leading edge for an experimental BAE concept jet. ●

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Questions?

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Thank You!