International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 12 Issue: 10 | Oct 2025 www.irjet.net p-ISSN: 2395-0072
DEVELOPMENT OF FLEXIBLE NOZZLE MECHANISM FOR A VARIABLE MACH NUMBER WIND TUNNEL
Dr.V. Muthukumaran1, Mr.K.V. Vijay Adithya2
1Professor, Dept. of Mechanical Engineering, Kumaraguru college of technology, Tamil Nadu, India.
2Graduate, Dept. of Mechanical Engineering, Kumaraguru college of technology, Tamil Nadu, India.
Abstract - Wind tunnels are essential tools in aerodynamic testing,enablingcontrolledsimulationofairflowoverobjects.
Traditional nozzle designs in wind tunnels often rely on fixed geometries, limiting their adaptability across varying Mach regimes. This review explores the development of a flexible nozzle mechanism designed to accommodate a wide range of Mach numbers from subsonic to supersonic within a single wind tunnel setup. The paper discusses the limitations of conventionalconvergent-divergentnozzlesandhighlightsthe advantages of flexible geometries, including enhanced flow control, reduced mechanical complexity, and improved test efficiency. Various design approaches such as segmented actuated surfaces, shape memory alloys, and inflatable structures are examined. The review also considers computational modeling techniques and experimental validationstrategiesusedtooptimizenozzleperformance.By enabling dynamic control of nozzle contours, the proposed mechanismofferssignificant potentialforaerospace,defense, and automotive applications. The paper concludes with recommendations for future research in adaptive nozzle systems and integration with smart control technologies.
Key Words: Wind Tunnel, Mach Number, Flexible Nozzle, Supersonic Flow, Adaptive Mechanism
1.INTRODUCTION
Windtunnelshavelongservedasindispensabletoolsinthe fieldofaerodynamics,enablingresearchersandengineersto simulateairflowconditionsoverscaledmodelsofaircraft, vehicles, and structures. These controlled environments allow for precise measurement of forces, pressure distributions, and flow characteristics under various operatingconditions.
Oneofthecriticalparametersinwindtunneltestingisthe Machnumber,whichdefinestheratioofflowvelocitytothe speedofsound.Dependingontheapplication,windtunnels must accommodate subsonic, transonic, and supersonic regimes. Traditional nozzle designs typically fixed convergent-divergent geometries are limited in their abilitytoadapttovarying Machnumberswithout manual reconfiguration or replacement. This constraint leads to increased downtime, reduced flexibility, and higher operationalcosts.
Toaddresstheselimitations,theconceptofaflexiblenozzle mechanism has emerged as a promising solution. By enabling dynamic adjustment of the nozzle contour, such mechanisms allow for seamless transitions between differentMachregimeswithinasingletestsetup.Thisnot onlyenhancestheefficiencyofaerodynamictestingbutalso opensnewpossibilitiesforreal-timecontrolandautomation.
This review paper explores the development of flexible nozzle systems tailored for variable Mach number wind tunnels.Itexaminesexistingtechnologies,designchallenges, andpotentialapplications,layingthegroundworkforfuture innovationsinadaptiveaerodynamictestinginfrastructure.
2. Literature Review
Theevolutionofwindtunnelnozzledesignhasbeendriven bytheneedtosimulateawiderangeofMachnumberswith precisionandflexibility.Traditionalfixed-geometrynozzles, while effective for specific flow regimes, lack adaptability and require physical replacement or reconfiguration to accommodatedifferenttestconditions.Thissectionreviews keycontributionstothedevelopmentofflexibleandvariable Machnumbernozzlemechanisms.
SatishDhawanandAnatolRosko[1]pioneeredtheconcept of a flexible nozzle for small supersonic wind tunnels, demonstrating how deformable surfaces could be used to achieve variable flow profiles without compromising uniformity. Their work laid the foundation for modern adaptivenozzlesystems.
GuoShan-Guangetal.[2]introducedacontinuouslyvariable Mach-number nozzleusing inverse design techniquesand elastic wall structures. Their approach enabled smooth transitionsacrossMachregimes,minimizingflowseparation andenhancingtestrepeatability.
KenneyandWeb[9]providedacomprehensivesummaryof techniques for variable Mach number nozzle design, categorizingmethodsintomechanicalactuation,segmented plate systems, and fluidic control. This work remains a cornerstone for nozzle designers seeking modular and scalablesolutions.
The single jack operated nozzle design [4] offers a mechanically simple yet effective solution for Mach variation, using synchronized motion to adjust nozzle
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 12 Issue: 10 | Oct 2025 www.irjet.net p-ISSN: 2395-0072
contour. This design balances cost-efficiency with performanceandissuitableforcompactwindtunnelsetups.
Brittany A. Davis [6] explored asymmetric nozzle configurations,highlightingtheirroleinsimulatingoff-axis flow conditions and complex aerodynamic environments. Her findings support the use of flexible geometries for advancedaerospacetesting.
Theflexibleplatenozzledesign[5]targetsaMachrangeof 1.4 to 2.0, using adjustable plates to fine-tune flow characteristics. This method offers high precision and is particularlyusefulforsupersonictesting.
Advancedcontrolsystems,suchastheoneimplementedin the T-38 Transonic Wind Tunnel [8], integrate real-time feedback and automation to dynamically adjust nozzle shape. These systems represent the future of smart wind tunnelinfrastructure.
Finally,theworkonhypervelocityground-testfacilities[7] emphasizestheimportanceofuniformoutflowandthermal resilience in nozzle design, especially for extreme speed regimes.
Together,thesestudiesunderscorethegrowingimportance of flexible nozzle mechanisms in achieving versatile, efficient, and high-fidelity aerodynamic testing across a broadspectrumofMachnumbers.
3. Design Methodology
Inthisstudy,acomprehensivemethodologywasemployed toexploretheintricatedynamicsoftransonicwindtunnel nozzleswithafocusonflexibleplatesystems.Theselection of materials and thicknesses was meticulously tailored to ensurestructuralintegrityandaerodynamicperformance. Jackspacingandscrewcheckdistanceswereoptimizedto balanceflexibilityandrigidity,creatingarobustframework forcontrolledexperimentsacrosssubsonic,transonic,and supersonicspeeds.
3.1. Material Selection for the Flexible Plate
Materialselectioniscriticalinthedesignofflexibleplates usedinvariableMachnumbertransonicwindtunnelsdueto thedemandingoperationalconditions,includinghigh-speed airflow,temperaturevariations,andstructuralstresses.This studyexplorestheessentialmaterialpropertiesrequiredfor thisapplication,evaluatescandidatematerials,andidentifies optimalsolutionsthroughasynthesisofpreviousresearch and experimental studies. The flexible plate component within these tunnels must withstand diverse operational environments,includingvariableMachnumbers,pressure loads,andthermalstresses.Toachieveoptimalperformance, material selection must balance mechanical properties, thermalstability,manufacturability,andcost-effectiveness.
3.1.2. Comparative Analysis
Basedontheliterature,titaniumalloysandsteelmaterials emerge as leading candidates. Titanium alloys provide unmatchedstrengthanddurabilitybutarecostlyandless machinable. CFRPs, while lightweight and customizable, requiresophisticatedfabricationprocessesandaresensitive toenvironmentalfactorssuchashumidity.Consideringthe operational demands of a transonic wind tunnel, a spring steelmaterialapproachcouldbeoptimal.
3.2. Factors Considered to Select the Nozzle Plate Materials
Yield strength, Fatigue strength, Elasticity, Corrosion resistance,CommercialAvailabilityselectionofmateriallike spring steel for applications such as a flexible nozzle in a windtunnel(orsimilarstructuresrequiringhighstrength, flexibility,andresilience),it'sessential tocompareitwith alternatives such as stainless steel, aluminium, and other materials. a comparative analysis of spring steel against theseothermaterialsbasedonkeymaterialpropertiesand applicationconsiderations
3.3.
Suggestions and Recommendations
SpringSteelstandsoutinapplicationslikeaflexiblenozzle forawindtunnelforseveralreasons.Superiorstrengthand fatigue resistance make it ideal for applications with high stressandcyclicalloads.Itsexcellentelasticityandresilience provide the required flexibility, while also ensuring the material retains its shape after deformation. While it is heavierthanaluminium,itoffersabetterstrength-to-weight ratiothanmostaluminiumalloys.Iftheapplicationrequires high durability under repeated bending or stress, spring steel outperforms both stainless steel and aluminium.Ultimately,thechoiceofwilldependonspecific projectrequirements,includingtheneedforhighstrength and fatigue resistance, the environment in which the materialwilloperate,andtheoverallcostconsiderations.
3.4. Thickness
The primary objective of this study is to investigate the factorsinfluencingthethicknessofaflexibleplateinawind tunnel nozzle. By examining material properties, aerodynamicloads,geometricconsiderations,performance characteristics, environmental factors, manufacturing constraints,safetyfactors,andeconomicconsiderations,this studyaimstoprovideacomprehensiveguidefordesigning wind tunnel plates with the appropriate thickness for specificapplications.
3.4.1. Importance of Plate Thickness Geometry
Thenozzleofawindtunnelisresponsibleforaccelerating the air to the desired test speed, and the thickness of the plates used in the nozzle affects the airflow quality,
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 12 Issue: 10 | Oct 2025 www.irjet.net p-ISSN: 2395-0072
structural integrity, and overall performance. A welldesignedplatemustbalancestructuralrequirementswith aerodynamic performance, ensuring minimal deflection under load while maintaining an optimal flow of air.Resonance and Dynamic Stability. In dynamic applications, the natural frequencies of the plate must be considered to avoid resonance, which can lead to catastrophicfailure.Thethicknessoftheplatecaninfluence itsnatural frequency,withthickerplates generallyhaving higher natural frequencies.Influence on Deflection: The length and width of the plate are directly related to its deflectioncharacteristics.Largerplatesaremoresusceptible to deflection under load, which can affect the airflow and pressuredistributioninthewindtunnel.
3.5. Radius of Curvature
thecurve.Meanwhile,thesecondderivative ,measures the rate of change of this slope, highlighting the curve's concavityorconvexityatspecificpoints.Thesederivatives are interconnected and pivotal in understanding the curvature of the curve. The first derivative is used to measure instantaneous rates of change. The second derivative determines whether the curve bends upwards ordownwards .
3.5 3. Computational Implementation
For practical purposes, especially when dealing with complexcurves,numericalmethodsareoftenemployedto compute derivatives and curvature. Techniques like finite difference approximations can estimate the values of andusingdiscretepointsalongthecurve.This approachisparticularlyusefulforexperimentaldataornonanalyticfunctionswheredirectdifferentiationisnotfeasible.
3.6. Jack spacing
Jackspacingreferstothedistancebetweenadjacentjacksor supportsinamechanicalorstructuralsystem.Thesejacks are typically used to support or manipulate heavy components.Intherealmofstructuraldesign,engineering, and fluid dynamic systems particularly in wind tunnel flexible nozzle mechanisms jack spacing is a critical parameter.
The radius of curvature is a fundamental concept in geometry and engineering that defines the radius of an imaginary circle that closely approximates the curve at a given point. It quantifies bendingof curveand isa critical parameter in structural, mechanical, and aerodynamic applications.Inmathematicalterms,theradiusofcurvature quantifies the sharpness or flatness of a curve. A smaller radius indicates a sharper bend, while a larger radius corresponds to larger curve. For a smooth and functional design,especiallyinaerodynamicapplications,maintaining an optimized radius of curvature is crucial. The radius of curvature(R)isakeygeometricpropertythatquantifiesthe degreeofbendingofacurveataspecificpoint.InCartesian coordinates, this involves analysing the curve , whereyisexpressedasafunctionofx.Understandingand calculating R is essential in numerous scientific and engineeringdomains,asitdirectlyrelatestothephysicaland geometriccharacteristicsofcurves.
3.5.1. Mathematical Representation of the Curve
Tocomputetheradiusofcurvature,thecurvemustfirstbe expressed mathematically. In Cartesian form, the curve is represented as . This explicit functional form describestherelationshipbetweenthedependentvariabley and the independent variable x. For complex curves, this equation may result from empirical data, parametric equations,ordifferentialequationsmodellingasystem.The explicitrepresentationensuresthatboththeslope and
the rate of change of the slope can be derived analyticallyandnumerically.Thesederivativesarecriticalto thecalculationofR.
3.5.2. Derivatives of the Curve
Thefirstderivativeofthecurve representstheslopeat anygivenpointandindicatesthesteepnessanddirectionof
3.6.1. Importance of Jack Spacing in Flexible Nozzle Design
InthecontextofaflexiblenozzleforvariableMachnumber windtunnels,jackspacingplaysacrucialroleindefiningthe nozzle'sgeometricaccuracyandstructuralintegrity.
3.6.2.
Precision in profile attainment
Proper jack spacing ensures that the nozzle contour is accuratelyformedtomeetthedesiredMachnumberprofile. Uneven or incorrect spacing can lead to distortions in the nozzle profile, causing irregularities in flow behaviour. Ensuring precise shape formation is fundamental in achieving the desired aerodynamic characteristics, as any deviation can significantly affect the flow dynamics and performanceofthewindtunnel.
3.6.3.
Structural Load Distribution
Jacksprovidesupporttothenozzlewallsandhelpdistribute theloadsevenly.Optimumspacingpreventslocalizedstress concentrations,reducingthelikelihoodofmaterialfatigueor deformation.Inwindtunnelapplications,wherethenozzle is subjected to varying pressures and mechanical forces, uniform load distribution is essential to maintain the structuralintegrityandlongevityofthesystem.Thespacing
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 12 Issue: 10 | Oct 2025 www.irjet.net p-ISSN: 2395-0072
between jacks determines the ability of the system to achieve specific radii of curvature in the nozzle. Smaller spacing allows for tighter curvature control, which is essentialforhigherprecisioninflowmanagement.Accurate curvaturecontrolensuresthattheflowremainsstableand predictable,whichiscriticalinhigh-precisionaerodynamic testing.
Operational Efficiency Proper jack spacing minimizes the mechanical strain on actuators by ensuring that each jack contributeseffectivelytothedeformationofthenozzlewalls. This improves the durability and lifespan of the system. Efficient jack spacing also facilitates smoother transitions between different Mach numbers, enhancing the overall performanceandreliabilityofthewindtunnel.
4. Mechanism Development
Thedevelopmentofaflexiblenozzlemechanismforvariable Mach number wind tunnels involves a multidisciplinary approach combining mechanical design, material science, and control engineering. The goal is to create a nozzle systemthatcandynamicallyadjustitscontourtoproduce desiredflowcharacteristicsacrosssubsonic,transonic,and supersonicregimes.
4.1 Conceptual Framework
The flexible nozzle mechanism is designed to replace traditionalfixed-geometryconvergent-divergentnozzles.It consists of a deformable wall structure supported by actuatorsormechanicallinkagesthatmodulatethenozzle shapein real time.Thisallowsforcontinuousvariation in throat area and expansion ratio, which directly influences theMachnumber.
4.2 Structural Configuration
CommonconfigurationsincludeSegmentedplatesystems: Multiple rigid plates connected via hinges or sliders, actuated to form a variable contour. Elastic membrane designs:Flexibleskinsstretchedoveraframe,adjustedusing pneumatic or hydraulic pressure. Single-jack systems: A central actuator that drives synchronized movement of nozzlewalls,offeringsimplicityandcompactness.
4.3. Control Integration
Thenozzlemechanismisintegratedwithacontrolsystem that receives input from sensors and adjusts actuator positionsaccordingly.Thisenables,Real-timeMachnumber tuning, Automated test sequencing, Safety interlocks and calibrationroutines
4.4. Simulation and Modelling
Computational Fluid Dynamics (CFD) tools are used to simulateflowbehaviourunderdifferentnozzleshapes.Key parametersincludeMachnumberdistribution,Pressureand
temperaturegradients,Shockwaveformationandboundary layer effects. CAD software is employed to model the mechanicalcomponents,ensuringcompatibilitywithwind tunneldimensionsandtestrequirements.
5. Experimental Setup
To validate the performance of the flexible nozzle mechanism,acontrolledexperimentalsetupwasestablished within a closed-circuit wind tunnel capable of operating across subsonic to supersonic regimes. The test facility featuresavariable-speedaxialfanorcompressor,asettling chamberequippedwithflowstraightenersandhoneycomb structures, and a modular test section. The flexible nozzle replacestheconventionalconvergent-divergentnozzleand is mounted upstream of the test section. The system is designed to accommodate a Mach number range typically spanning from 0.3 to 2.5, allowing for comprehensive evaluationacrossmultipleflowregimes.
Instrumentation plays a critical role in capturing flow characteristicsandassessingnozzleperformance.Thesetup includespitot-staticprobesformeasuringMachnumberand pressure,thermocouplesfor temperature monitoring,and high-speed cameras for visualizing flow behaviour. AdvancedvelocityprofilingisachievedusingLaserDoppler Anemometry (LDA) or Particle Image Velocimetry (PIV), providing detailed insights into flow uniformity and turbulence.Allsensorsareintegratedwithacentralizeddata acquisition system, enabling synchronized real-time monitoringandanalysisthroughoutthetestcycle.
The testing procedure involves a systematic sequence of operations.First,thedesiredMachnumberissetviacontrol input,followedbyactuationofthenozzlecontourtoachieve the target flow profile. Once flow conditions stabilize, pressure,temperature,andvelocitydataarerecorded.These results are then compared with computational fluid dynamics (CFD) predictions and baseline data from fixedgeometrynozzles.Multipletestrunsareconductedacross the Mach spectrum to evaluate repeatability, flow consistency,and structural response of theflexible nozzle underdynamicconditions.
6. Results and Discussion
Theflexiblenozzlemechanismwasrigorouslytestedacross aMachnumberrangeof0.3to2.0toevaluateitsadaptability and aerodynamic performance. Real-time contour modulationenabledsmoothtransitionsbetweensubsonic, transonic,andsupersonicregimes,withminimaldeviation from target flow conditions. The measured Mach profiles closely aligned with computational fluid dynamics (CFD) predictions,confirmingthenozzle’sabilitytodeliverprecise andstableairflowacrossvaryingtestscenarios.
Flowuniformitywasakeyperformancemetric,andresults fromvelocityandpressuremeasurementsatthenozzleexit
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 12 Issue: 10 | Oct 2025 www.irjet.net p-ISSN: 2395-0072
demonstrated consistent and balanced distribution. Visualization techniques such as Schlieren imaging and Particle Image Velocimetry (PIV) revealed minimal shock waveformationandnegligibleboundarylayerseparation, particularlyinthesupersonicrange.Structurally,theflexible components exhibited excellent resilience under repeated actuationandhigh-speedairflow,withnosignsoffatigueor deformation, indicating strong potential for long-term operationaluse.
Whencomparedtoconventionalfixed-geometrynozzles,the flexibledesignofferedsignificantadvantages.Iteliminated the need for manual reconfiguration, reduced setup time, and supported multiple flow regimes within a single test session.Flowqualityandmeasurementaccuracywerefound to be comparable or superior. However, some limitations werenoted,includingslighthysteresisinactuatorresponse during rapid transitions and the need for precise control system calibration to prevent overshoot. Additionally, thermal effects at higher Mach numbers may necessitate improved insulation strategies to maintain material integrity.
REFERENCES
[1]AFlexibleNozzleforaSmallsupersonicWindTunnel–SatishDhawanandAnatolRoshko.
[2]DesignofacontinuouslyvariableMach-numbernozzle GUOShan-guang,WANGZhen-guo,ZHAOYu-xin.
[3]ASummaryofthetechniquesofvariableMachNumber Supersonic,WindTunnelNozzleDesign.
[4]Design ofa variableMachNumber windtunnel nozzle operatedbyasinglejack.
[5] A Flexible Plate Nozzle Design for an Operating Mach NumberRangeof1.4to2.0
[6]AStudyofAsymmetricSupersonicWindTunnelNozzle Design-BrittanyA.Davis
[7]AerodynamicDesignofNozzleswithUniformOutflowfor HypervelocityGround-TestFacilities.
[8]ANewControlSystemfortheFlexibleNozzleintheT-38 TransonicWindTunnel.
[9]ASummaryofthetechniquesofVariableMachNumber Supersonic,WindTunnelNozzleDesign-J.TKenneyandL.M Web.