Aeroacoustic Simulation Delivers Breakthroughs in Aircraft...

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AeroacousticSimulationDeliversBreakthroughsinAircraftNoiseReductionByBruceJenkins,PrincipalAnalyst,OraResearch

Aircraft manufacturers face increasinglystringent standards for reducing communitynoise. Conventional aircraft developmentmethodsbasedonengineeringexperience,pastdesignsandflighttestingwillnotsufficetomeetfuture noise reduction targets. ComputationalFluid Dynamics (CFD) software based on so-called Reynolds-averaged Navier-Stokes (RANS)methods has revolutionized aircraft aero-dynamicsengineering,butisinsufficientforhigh-fidelity aeroacoustic simulation. However, theLattice-Boltzmann based technology of ExaCorporation’s PowerFLOW software providesaeroacousticsimulationaccuracycomparabletowindtunnelsandflighttesting.Today,PowerFLOW’suniquevalue and benefits for aeroacoustic simulation are being proven in practice byNASA, Embraer and othersdeployingthesoftwaretoachievebreakthroughsinaircraftnoisepredictionandmitigation.

Aircraft manufacturers face increasingly stringent standards for reducing community noise

Aircraftnoise,alreadyaproblemformanycommunitieslocatednearmajorairports,willonlygetworsewiththecontinuinggrowthinairtravel.Thus,ontopofaircarriers’demandsformorefuel-efficient,cheaper-to-operateairplanes,commercialaircraftmanufacturersfaceincreasinglystringentrequirementstoreducethe“communitynoise”producedbytheiraircraft.Already,communitiesaswellasindividualairportsimposenoiseregulationsthatmayaffectwhichaircraftareallowedtolandatgiventimes,andchargeairlinesafeeifanyoftheir aircraft are too noisy. All this has made noise reduction a critical competitive factor for aircraftmanufacturerstoday.AccordingtoastudyledbyNASALangleyResearchCenter,“Thecontinuousgrowthinairtravelhasledtoanincreaseincommunitynoiseexposure,resultinginstricterairportregulationsnationallyandinsomecasesalsoregionally.Expectedfuturenoiserestrictionswillinevitablyleadtothedevelopmentofoverallquieteraircraftdesigns.”1

1FaresE.,CasalinoD.,ExaGmbH,andKhorramiM.,NASALangleyResearchCenter,“EvaluationofAirframeNoiseReductionConceptsviaSimulationsUsingaLatticeBoltzmannApproach,”AIAAAviationandAeronauticsForum2015.

Simulatedradiatedsoundfieldfromafull-scalebusinessjetduringlandingwithflapsandmainlandinggearsdeployed.Credit:NASALangleyResearchCenter.

AeroacousticSimulationDeliversBreakthroughsinAircraftNoiseReduction

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Communitynoisehastwomainsources:enginenoiseandairframenoise.Airframenoiseiscausedprincipallybyairflowaroundtheaircraft’slandinggear,andaroundhigh-liftdevicessuchaswingflapsandslats.Themainsources of engine noise are theenginefanandthejetdownstreamof the engine. The figure on therightvisualizesthesenoisesourcesbased on predictions from Exa’sPowerFLOW code, using some ofthe unsteady flow visualizationtechniques available inPowerFLOW. In addition, a factorknownas“installationnoise”—thenoise created by interactions ofthejetfromtheengineaswellasthe main landing gear withcomponents of the high-liftwing,inparticulartheflaps—canbeasignificantcontributortooverallnoise.

Overthepast20years,aircraftenginemanufacturershavemadesignificantprogressinreducingenginenoisethroughadvancessuchashigh-bypassturbofansandinnovativenozzlegeometries.Thishaspromotedairframenoise to themosturgentchallengenow—especiallyduring landingapproach,whennoiseproducedby theairframe is as loudas, or even louder than, propulsionnoise.According to the study ledbyNASA LangleyResearchCenter,“Airframenoiseconstitutesamajorcomponentofthetotalnoisegeneratedbycontemporarycivilaircraft,especiallyduringlandingwhentheenginesaretypicallyatlowthrustsettings.”1

Atthesametime,mitigatingenginenoiseremainsimportantinreducingtakeoffnoise.Accordingtoastudyby Swen Noelting, Vice President, Aerospace, and Ehab Fares, Senior Technical Director of AerospaceApplications, bothwith CFD software developer Exa Corporation, “Despite huge reductions over decades,enginenoise isstill thebiggestcontributortocommunitynoiseduringtakeoff.Thereductionshavemostlybeenachievedbyincreasingthebypassratioofjetengines,whichcannotrealisticallybefurtherincreasedduetogeometricalconstraints.Therefore,significantresearchefforthasbeenputintobetterunderstandinganddirectlyreducingfanandjetnoise,themaincontributorstoenginenoise.”2

Addingtothechallengeofreachingaggressivenoisereductiongoalsisthefactthattheseareofteninconflictwith other performance objectives. For example, the goal of increased fuel efficiency can be achieved bymaking the engines larger, but the resulting increase in fan radiuswillmake the engine noisier. Similarly,reducingnoisefromhigh-liftdevicesmayimpacttheliftperformanceofanaircraft.

2Noelting,S.andFares,E.,“TheLattice-BoltzmannMethod:AnAlternativetoLESforComplexAerodynamicandAeroacousticSimulationsintheAerospaceIndustry,”SAETechnicalPaper2015-01-2575,2015,doi:10.4271/2015-01-2575.

Visualizationofthemainnoisesourcedofacommercialaircraft





Conventional aircraft development methods based on engineering experience, past designs and flight testing will not suffice to meet future noise reduction targets

Traditionally, aircraft engineering organizations have relied on experience from past aircraft designs, andempiricalmethodstomeetnoisetargets.Thereislittle,ifany,useofwindtunnelstoreduceaircraftnoise.Mostoftentheprocedurehasbeensimplytoengineertheaircraftwithahighsafetymarginwithrespecttonoiserequirements,andthenhopeitwillmeetcertificationrequirementsinflighttesting.

Butincreasinglystringentnoiseregulationsaremakingthesetraditionalprocessesinadequate—engineerswillnolongerbeabletodesigninenoughsafetymargintobeconfidenttheirnewaircraftwillmeetcertificationtargets.Windtunneltestingisseldom(ifever)aviablesolutionfornoiseoptimizationincommercialaircraftdevelopmentprograms,duetothefactthatacompleteaircraftwithallrelevantnoisesourcescannotbetestedinawindtunnelatascalethatwouldadequatelycapturethenoisesources.Testingofindividualcomponents–suchaslandinggearsandhigh-liftdevices–ispossibleinwindtunnelsbutalsooflimiteduseduetotimeandcostconstraintsandtheinabilitytocaptureinstallationeffects.

However,thealternativetowindtunnels—usingdigitalsimulationtotestrealisticconceptsforairframenoisereduction—hasbeenachallengingtask.Toaccuratelypredictandmitigateairframenoise,forexample,thelandinggear’scomplexgeometryhastoberepresentedathighfidelity inthesimulationmodel,sinceevensmallgeometrydetailscanbesignificantnoisecontributors.Inaddition,theentireaircrafthastobesimulated,inordertoidentifythecomplexinteractionsamonglandinggear,wingsandothermajoraircraftcomponents.ThishasprovedtobeanextremelychallengingtaskfortraditionalRANS-basedCFDtools.

CFD based on Reynolds-averaged Navier-Stokes methods revolutionized aircraft aerodynamics engineering, but is insufficient for high-fidelity aeroacoustic simulation

Noelting and Fares of Exa note that significant progress has beenmade over the past several decades insimulatingaerodynamicflowsusingCFD,andthatthishasfundamentallychangedthedesignprocessintheaerospace industry. But the use of CFD has been focused mostly on modeling the aircraft in cruiseconfiguration—notwithflapsextendedandlandinggearsdeployed.CFDhashadmuchlessimpactformorecomplexconfigurationsotherthanthecomparativelysimplegeometryofanaircraftincruisecondition.

MajortechnologicallimitationsremaintoexpandtheuseofCFDtomorecomplexconfigurations.“ThestateoftheartinCFDisbasedonReynolds-averagedNavier-Stokes(RANS)methodswhichhaveprovenaccuracyandreliabilityforflowconditionsatornearthedesignpointincruiseconfiguration,”NoeltingandFarespointout. “The usability of thesemethods is generally limited today, however, to relativelywell-behaved flowswithoutsignificantflowseparationorunsteadiness.WhileitisexpectedthatLargeEddySimulations(LES)andhybridRANS-LESmethodswill eventuallybeable toaddress these typesof inherentlyunsteady flows, thecomputationalcostassociatedwithrunningLargeEddySimulationsforanindustrialapplicationisexpectedtobeprohibitivelylargeeveninthedecadestocome.”





AnotherchallengetraditionalRANS-basedCFDmethodsarefacingisthehandlingofcomplexgeometriesandgrid generation. Creating the computational grids for configurations that are typically associated withseparatedflows,suchasfullydetailedhigh-liftwings—possiblyincludingfairingsandbrackets,nacellesandlandinggears-remainsoneofthegreatestbottlenecksforcurrentCFDtools.Inaddition,strongdependenceofresultsonmeshquality,non-convergenceofsimulationsandtherequirementfordeepCFDexpertiseareallcriticalfactorsslowingtheexpansionoftheapplicationofCFDintheaerospacedevelopmentprocess.

Oneof theapplications thathave shownvirtuallynoproductiveuseofCFD in thedevelopmentprocess isaeroacousticsandcommunitynoise.Thisincludesairframenoisefromlandinggearsandhigh-liftcomponents,andjetandinstallationnoise—allofwhicharegenerallyaddressedtodayonlyinflighttesting.ThelimitationsoftraditionalmethodshavemadeproductiveCFDuseinthisareaimpossibleuntilnow.ThisisnowchangingwiththeavailabilityofLattice-BoltzmannbasedcodessuchasExa’sPowerFLOW.

Lattice-Boltzmann technology of Exa’s PowerFLOW provides aeroacoustic simulation accuracy comparable to wind tunnels and flight testing

Exa’sPowerFLOWsoftware isgaining increasing recognitionas the firstCFDsolutioncapableofeffectivelysimulatingthefullcomplexitiesofthedesignfactorsthatdetermineaircraftnoise,andprovidingguidancefornoisemitigation.AmethodologydevelopedinpartnershipwithNASAhasdemonstratedthatExa’ssoftwaretechnologycanbeusedinawaythatdeliversaccuracycomparabletowindtunneltestingandflighttesting.Experiments show that with PowerFLOW, users are able to predict airframe noise propagated to groundobserverswithinanerrorrangeof1to2decibelsfromphysicalexperiments—resultsthathavebeenextendedtoenginenoisepredictionaswell.

NoeltingandFaresexplain thatExa’s technologicaldifferentiation isgrounded in “non-traditionalmethodssuchtheLattice-Boltzmannmethod(LBM),combinedwiththebestfeaturesofhybridturbulencemodeling.”LBMnotonlyhasthepotentialtotackletheadvancedflowphysicsrequired,butalsooffersnewpossibilitiesforfullyautomaticvolumemeshgenerationandparallelization.

“Numerical flow simulations using the Lattice-Boltzmannmethod have evolved over the past ten years tobecomeastandardCFDtoolinthedailyaerodynamic,aeroacousticandthermalengineeringdesignpracticeintheautomotive industry,”theynote.“TheLBMapproachhasdemonstratedahigh levelofaccuracyandefficiencyinmanypreviouspublications.Morerecently,themethodalsoreceivedincreasingattentionfromtheaerospacesectoraddressingindustriallyrelevantapplicationsonrealisticcomplexfullairplaneandenginegeometries.”

TheLattice-Boltzmannmethod,includingitsimplementationinExa’sPowerFLOW,isbasedonkinetictheory.ArelativelynewCFDtechnology,LBMhasonlybeendevelopedoverthe last25to30years. IncontrasttomethodsbasedontheNavier-Stokes (N-S)equations,LBM isbasedonasimplerandmoregeneralphysicsformulation.Itsmotivationistosimulateafluidatamicroscopiclevelwherethephysicsissimplerandmoregeneralthanthemacroscopic,continuumapproachtakenbytheNavier-Stokesequations.





Further,LBMcangenerallybecombinedwithvariousturbulencemodelingapproachesincludingastandardturbulence model, an LES subgrid scale model and also hybrid approaches. The clear advantage of LBMmethods is the very high temporal resolution, inherently efficient unsteady simulation algorithm, and lowdissipationanddispersionofthenumericalscheme.Theseadvantagesresultinaboutoneorderofmagnitudegreater(insomecasesevenmuchmore)computationalefficiencythanCFDsolutionsbasedonclassicalNavier-Stokessolutionsofcomparablequality.

Anotherkeyadvantageof theLattice-Boltzmannmethod is thehighefficiencyofcomputationsonmoderncomputeclusterswithhundredsorthousandsofinterconnectednodesandtensofcomputationalcorespernode,duetothepredominantlylocalnatureofcomputationaloperationswhichdramaticallyreducesthecore-to-corecommunicationsrequirementscomparedwithtraditionalRANSmethods.

Insummary,themaindifferencesbetweenN-S-basedmethodsandLBMare:

• LBMisbasedonasimplerrepresentationoftheflowphysics;thus,thealgorithmicimplementationislesscomplicated.

• LBM is most efficiently implemented on Cartesian grids. Cartesian grids allow for very robustautomatedgridgenerationofcomplexgeometries.

• LBM is inherently unsteady. For steady-state solutions, it is aboutoneordermoreexpensive thansteady-state RANSmethods, but for unsteady solutions, it is about one order less expensive thancomparableN-S.

• LBM offers low numerical dissipation, which makes it well suited for simulations of wakes anddetachedflows,andforaeroacoustics.

• LBM methods are easily parallelized and can run efficiently on modern HPC architectures withthousandsofcomputationalcores.

Unique value and benefits of PowerFLOW for aeroacoustic simulations

Aeroacoustic simulations, such as the prediction of noise generated by landing gears and high-lift devicesduring approach and take-off are an almost ideal application for LBM, Exa’sNoelting and Fares point out.Acousticsimulationsbydefinitionhavetobeunsteady,andtheextremelylownumericaldissipationofLBMenablesthecaptureofboththehydrodynamicpressurefluctuationsonthecomponentsurfacesresponsiblefor the noise generation, and the resulting coherent acoustical pressure fluctuations emanating from thestructurewhichareresponsibleforthefar-fieldcommunitynoise.Inaddition,thegeometriesthatmustbesimulatedforairframenoisecasestendtobehighlycomplexandcannotbesimplifiedforsimulation,sinceevensmallgeometrydetailsmaycontributesignificantlytothefar-fieldnoise.





Likewise, LBMoffersanumberofbeneficialproperties formitigating jet, fan and installation noise. First, the lowdissipation characteristic of the method is a fundamentalenabler to capture the wake of a jet or propeller withsufficient accuracy. Second, the simplicity with regard toformulation of boundary conditions in the LBM approachallows efficient implementation of techniques to simulaterotatingormovinggeometries.TheLBMimplementationinPowerFLOW offers a sliding-mesh technique that enablesvery accurate simulations of rotating geometries, ideal forsimulationsofpropellersorfans.

Exahasdevelopedthemethodologytosimulateairframeandenginenoiseinamulti-yearco-operationwithNASA.Initially,isolatedcomponentssuchasnoseandmainlandinggearsweresimulatedandthencomparedtowindtunnelteststoensurethatallrelevantnoisesourceswerecorrectlycaptured.TheimageontherightshowstheflowstructuresandacousticwavesaroundabusinessjetmainlandinggearthatwasevaluatedinthepartnershipwithNASA.3

ThenextstepintheNASA-Exapartnershipincludedtheevaluationofnoisegeneratedhigh-liftdevicessuchasflapedges,and thedevelopmentofconcepts to reduce thesenoisesources.4The imageon the leftbelowshowspressure fluctuationsonthesideedgeof theflapwhichareoneof themainoverallcontributorstoairframenoise.Inaddition,installationeffectswereidentifiedbyinvestigatingtheinteractionsofadeployed

landinggearwiththehigh-liftcomponentsofthewing.

Using this methodology, PowerFLOW can be used toanalyzethelandinggear’scontributiontooverallaircraftnoise. This allows an aircraft manufacturer to give itslanding-gearsupplierdetailedengineeringdataonhowtoconfigure and size the landing gear to achieve noisetargets.

A number of studies have also been performed withPowerFLOWtovalidatethesimulationofjetnoiseandfan

noise.Forexample,simulationandcomparisontophysicalexperimentforoneofthesetpointsforthewell-knownSMC000testcaseshowedgoodagreementofbothmeanflowandfluctuatingcomponentsoftheflow.

3 Keating, A., Dethioux, P., Satti, R., Noelting, S., Louis, J., Van de Ven, T., and Vieito, R., “Computational Aer-oacousticsValidationandAnalysisofaNoseLandingGear,”AIAAPaper2009-3154,May2009.4FaresE.,CasalinoD.,ExaGmbH,andKhorramiM.,NASALangleyResearchCenter,“EvaluationofAirframeNoiseReductionConceptsviaSimulationsUsingaLatticeBoltzmannApproach,”AIAAAviationandAeronauticsForum2015.

Pressurefluctuationsonthedeployedflapsofabusinessjet

Flowstructuresaroundthenoselandinggearofabusinessjet,highlightingthemainnoisesources.





Exaalsoparticipatedinamajorstudy,againledbyNASA,toimprovesimulationcapabilitiesforfannoiseandPowerFLOWwasidentifiedasthemostpromisingsolutionforthisapplicationaswell.5

In addition to predicting the overall noise levels of an aircraft and its components, Exa has developedmethodologiestoidentifythesourcesofthisnoise—forexample,toidentifyexactlywhichpartsofthelandinggeararecausingnoise—thatgiveuserstheinsightneededtoremedytheproblem.Itssoftwarecanthenbeusedtotestvariousnoisereductionconceptsonalandinggeardesign.

Forthefuture,aircraftmanufacturerswillhavetoaccomplishmajorchangesinthearchitectureoftheiraircraftinordertomeetlong-termnoisereductiongoals.SimulationtechnologieswiththecapabilitiesofPowerFLOWwillbeessential for that—thechangesneededwill simplybeoutside the scopeand reachof conventionalaircraftengineeringpractices.

NASA, Embraer proving PowerFLOW’s value for aircraft noise prediction and mitigation

ThebreakthroughbenefitsofExa’sPowerFLOWsoftwareforcommunitynoisepredictionandmitigationarealreadybeingprovenbyleadingcustomerstoday.Inearly2015NASAexpandeditsusageofPowerFLOWforthesimulationofconceptstoreduceaircraftnoisewithinNASA’sEnvironmentallyResponsibleAviation(ERA)project. PowerFLOW predictions had been successfully validated against high-fidelity wind-tunnel tests in

2013;then,afterthecancellationofaplannedflighttestdueto budget constraints of one of the ERA contract partners,NASAelected tousePowerFLOWsimulationsofa full-scaleaircraftwithflapandlanding-gearnoisetreatmentstoreachtheoriginalairframenoiseobjectivesoftheproject.

MehdiKhorrami,SeniorResearchEngineeratNASALangleyResearchCenter,said,“Weareraisingthebarwithfull-scalesimulations. This is challenging stuff, at the frontiers ofcomputational fluid dynamics. The simulations of the full-scaleaircraftwithnoisereductionconceptswillhelprecoverasignificantpartofthelossoftheflighttest.Inaddition,thesimulations provide valuable insight into the sources ofairframenoise.”6

Tohelpalleviatetheproblemofaircraftcommunitynoise,NASA’sEnvironmentallyResponsibleAviation(ERA)projectwithinitsAeronauticsResearchMissionDirectorateisperforminglarge-scaleaerodynamicsimulationsto develop and evaluate novel noise-reduction concepts for aircraft. Using the agency’s Pleiadessupercomputer,scientistsperformhigh-fidelitysimulationsoftheairflowaroundkeyairframecomponents.

5 Casalino D., Hazir A., Mann A., “Turbofan Broadband Noise Prediction using the Lattice Boltzmann Method,” AIAACEASAeroacousticsConference,June2016.6Pressrelease,2015

Noiseemanatingfromthelandinggearareaofabusinessjet.Installationofnoisereductionconcepts(bottomimage)clearlyleadtoreducedacousticfluctuations.





Theproject’srecentstudiestargetedthenoisegeneratedbythelandinggearandwingflaps,basedonan18%scalesemi-spanmodelofaGulfstreamaircraft[figureatleft].NASAreportsthatthesesimulationsprovidednewinsightsintothecomplexflowinteractionsaroundtheflapsandlandinggear,andhowtheyincreasethesoundfieldradiatingtowardtheground.EnabledbyNASA’ssupercomputingresources,theteamusedtheseinsightstodevelop,evaluateandrefineseveralviablenoise-reductionconcepts.

A joint report by NASA and Exa provides additional insight:“High-fidelityunsteadynumericalsimulationsofan18%scale,semi-span model of a Gulfstream aircraft in landingconfiguration (flap deflected at 39° with main landing geardeployed) were recently performed using a Detached EddySimulation(DES)approachwithinNASA’sFUN3Dunstructuredcompressible Navier-Stokes solver and a Lattice-Boltzmann-Very Large Eddy Simulation (LB-VLES) approach within ExaCorporation’s PowerFLOW solver [figure at right]. Thesimulations, which combined multiple components of acompleteaircraftincludingmainlandinggearinteractionwiththe flap side edge of a high-lift system, compared well withmeasured quantities (steady and unsteady surface pressuresandfar-fieldnoise).Whilethestudydemonstratedthegeneralfeasibilityofbothflowsolverstoaccuratelysimulate complex aeroacoustic interactions, the Lattice-Boltzmann algorithm provides a unique set ofadvantages in terms of computational efficiency, high frequency resolution and handling of very complexgeometricaldetails,thusmakingitanidealtoolforsimulatingvariousnoisereductiontechnologiesandtheireffectontheoverallaeroacousticcharacteristicsoftheconfiguration.”7

“Our high-fidelity simulations have enabled us to probe into the underlying noise-generationmechanismsassociatedwithflowoveraircraftflapsandlandinggear,andtodevelopandimproveseveralpromisingnoise-reductionconcepts,”saidNASA’sKhorrami.TheERAproject’shigh-fidelitysimulationscapturethecomplexaerodynamiceffectsthatimpactaircraftnoise,suchasvortexformation,bluffbodyflowseparation,andflowinteractions between multiple airframe components. The large-scale, time-dependent airframe noisesimulationswereperformedusingExa’sPowerFLOWLattice-Boltzmannflowsolver,with twobillionto fivebillion volumetric cells used to discretize the space surrounding the aircraft surfaces in the computationalmodel. All the ERA project’s simulations were performed on NASA’s Pleiades supercomputer usingapproximately3,000processorsfortwotofourweekseach,andresultedinseveralpetabytesofdata.

7Khorrami,M.R.,Fares,E.,andCasalino,D.,“TowardsFull-AircraftAirframeNoisePrediction:Lattice-BoltzmannSimulations,”AIAAPaper2014-2481,June2014

Illustrationof the impactof themain landinggearonnoisegeneratingpressurefluctuationsonthewing.





NASAreportsthattheERAprojectdemonstratedtheeffectivenessofthenoisereductiontechnologiesithasdevelopedthroughbothwindtunneltestingandsimulation.“Theproject’srecentsimulationeffortsrepresentamajorsteptowardpredictingtheradiatednoisefieldfromafullaircraftinlandingconfiguration,”accordingtoNASA.

AnotherpioneerisEmbraer,theworld’sthird-largestcommercialaircraftcompany, which in late 2014 significantly expanded its usage of Exa’sPowerFLOWsoftwaretohelpimprovebothaerodynamicandaeroacousticperformance of its new products [figure at right]. According toMauroKern,ExecutiveVicePresidentofEngineeringandTechnologyatEmbraer,“Embraer is always looking for innovative solutions to improve ourdevelopment processes. PowerFLOWwill help us analyze and eliminatenoisesourcesearlier inthedesignprocessthanhasbeenpossible inthepast.”

Conclusion

Aircraftnoise,alreadyaproblemformanycommunitieslocatednearmajorairports,willonlygetworsewiththecontinuinggrowthinairtravel.Thus,ontopofaircarriers’demandsformorefuel-efficient,cheaper-to-operateairplanes,commercialaircraftmanufacturersfaceincreasinglystringentrequirementstoreducethe“communitynoise”producedbytheiraircraft.

Community noise has twomain sources: engine noise and airframenoise. Significant progress in reducingengine noise over the past two decades has promoted airframe noise to themost urgent challenge now.Airframenoiseiscausedprincipallybyairflowaroundtheaircraft’slandinggear,andaroundhigh-liftdevicessuch aswing flaps and slats.Wind tunnel testing is seldom if ever a viable solution in commercial aircraftdevelopmentprogramsduetocostandtimeconstraints.Butthealternative—usingdigitalsimulationtotestandrefineconceptsforairframenoisereduction—isachallengingtask.Tobeeffective,theentireaircrafthastobesimulatedinordertoidentifytheinteractionsamonglandinggear,wingsandothercomponentsthatareamajorcauseofnoise.Inaddition,thelandinggear’scomplexgeometryhastoberepresentedathighfidelityinthesimulationmodel,sinceevensmallgeometrydetailscanbesignificantnoisecontributors.

Atthesametime,mitigatingenginenoiseremainsimportantinreducingtakeoffnoise.Inaddition,“installationnoise”—thenoisecreatedbyinteractionsoftheenginewithcomponentsofthehigh-liftwingcomponents,inparticular the flaps—can be a significant contributor to overall noise. Finally, noise reduction goals oftenconflictwithotherperformanceobjectives,sothattradeoffsmustbequantifiedandevaluated.

Traditionally,aircraftengineeringhasreliedonpastexperience,pastaircraftdesigns,andempiricalmethodsto meet noise targets. But increasingly stringent requirements are making these processes inadequate—conventionalmethodswillnotsufficetomeetfuturenoisereductiontargets.

Flowstructure visualizationaround thewingofanEmbraerregionaljetinhigh-liftconfiguration




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Thelongstandingalternative—CFDsoftwarebasedonReynolds-averagedNavier-Stokes(RANS)methods—hasrevolutionized aircraft aero-dynamics engineering, but its use has been restrictedmostly tomodeling thecomparativelysimplegeometryoftheaircraftincruiseconfiguration.Forsimulationsoftheaircraftwithflapsextendedand landinggearout,CFDhasbeenmuch lessusedbecauseof inherent limitations thatmake itimpracticalandinsufficientforhigh-fidelityaeroacousticsimulation.

Today, however, Exa’s PowerFLOW software is emerging as the first CFD solution capable of effectivelysimulatingthefullcomplexitiesofthedesignfactorsthatdetermineaircraftnoise.EnablingthiscapabilityisPowerFLOW’s technology, grounded in non-traditional methods such the Lattice-Boltzmann method,combinedwiththebestfeaturesofhybridturbulencemodeling.AmethodologydevelopedinpartnershipwithNASA recently demonstrated that Exa’s software technology delivers accuracy comparable towind tunneltestingandflighttesting,forbothairframenoiseandenginenoise.Now,inadditiontoNASA,PowerFLOW’suniquevalueandbenefits foraeroacoustic simulationarebeingproven inpracticebyEmbraerandothersdeployingthesoftwaretoachievenewbreakthroughsinaircraftnoisepredictionandmitigation.

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We aim to inform and guide professionals with fresh information about these technologies and their successfuladoptionandapplication.Weofferresearchandadvisoryservicestohelpengineeringorganizationsevaluate,selectand justify new technology investments, and to help technology providers qualify and quantify new marketopportunitiesandvalidatedemanddrivers.Ourgoal is to foster insightandaction tostrengthenthe industriesweserve.www.oraresearch.com

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