acoustics fluent simulation

1AeroacousticsModelingBy:SandeepSovani,Ph.D.SeniorConsultingEngineerFluentInc.,AnnArbor,MIMarch18th,2005PresentedatFluentLunchandLearnseminarseriesSt.John’sConferenceCenter,Plymouth,MI2Welcome!„FluentInc.’sLunch’N’LearnSeminarSerieszTopicalseminarsonleadingedgeCFDapplicationszHeldfrequentlyŠAeroacousticsModeling–March18,2005ŠFloWizard–April22,2005ŠUnsteadyFlowModeling–April29,2005ŠMultiphaseModeling–May20,2005zPurposeŠInformtheFLUENTcommunityaboutthesubjectfDiscussbasics,physics,theory,modelingtechniques,fToolsavailableinFLUENTtomodelthesubjectfExamples3Outline„AeroacousticsBasics„SimulationMethodszComputationalAeroacoustics(CAA)zSegregatedSource-PropagationMethods(SSPM)ŠFundamentalsŠVariationalMethodsŠBoundaryElementMethodsŠIntegralMethodszStochasticNoiseGenerationandRadiation(SNGR)„Summary„Bibliography„SimulationGuide4Basics:Acoustics„DefinitionszAcoustics=Thescientificstudyofsound[1]zSound=Pressurewavesradiatinginanymaterialmedium„HistoryzSoundwasrecognizedtobeawavephenomenonover2000yearsago![2]ŠChrysippus(Greekphilosoper,240BC)ŠVetruvius(Romanarchitectandengineer,25BC)„SoundhasessentialcharacteristicsofwaveszIthasa“source”ŠOscillatorydisturbancezIt“propagates”ina“medium”ŠTransportsenergywithouttransportingmatter5Basics:Acoustics„Source,Medium,Propagation,ReceiverSourceMediumWavePropagationSourceMediumWavePropagationReceiver6Basics:Acoustics„Acousticsissub-classifiedbasedon[2]zSourceŠAeroacousticsŠVibroacousticsŠEtc.zMediumŠHydroacousticsŠSeismologyŠEtc.zEtc…7Basics:Aeroacoustics„AeroacousticszSub-areaofacousticswherethesourceofsoundisfluidflow„CharacteristicszNomovingboundariesŠsuchaselectricspeakers,vibratingstrings,orvocalchordszUnsteadyfluidflowalwaysproducespressureoscillationsŠthereforeisinherentlyasourceofsound„ExampleszWhistleszHVACventnoisezAutomotivewindnoise8Basics:AeroacousticsSoundFlowAcousticMediumReceiverSourceSource≡TransientpressurevariationcausedbytheflowSound≡Pressurewavespropagatingintheacousticmedium9Basics:CharacteristicsofSound„SoundwaveshaveseveralkeyattributeszCompressiblephenomenonzWaveamplitudeisverysmallzSoundwavescarryonlyatinyfractionoftheenergycontainedinthemeanflowŠE.g.AcousticenergygeneratedbyBoeing747duringtake-offisnotenoughtoboilanegg!0204060801001201401.E-041.E-031.E-021.E-011.E+001.E+011.E+02Pressure(Pascal)SPL(dB)=refrmspp'20logSPL1025/102mNpref−×=1atm=1E+5Pa10Outline„AeroacousticsBasics„SimulationMethodszComputationalAeroacoustics(CAA)zSegregatedSource-PropagationMethods(SSPM)ŠFundamentalsŠVariationalMethodsŠBoundaryElementMethodsŠIntegralMethodszStochasticNoiseGenerationandRadiation(SNGR)„Summary„Bibliography„SimulationGuide11„OutputstypicallydesiredfromaaeroacousticsstudyzSourceStrengthsŠSourceRankingzFrequencySpectrumŠAtobserverzDirectivitySimulation:Objectives12Simulation:Aspects„ToobtainthedesiredoutputstwoaspectsneedtobesimulatedzSoundsourceŠProvidessourcecharacteristicsandrankingszSoundpropagationŠPropagationofsoundfromthesourcetothereceiverfRequiresinputofsourcecharacteristicsfProvides»Soundspectrumandreceiver»Sounddirectivity„Aeroacousticssimulationessentiallyinvolvescomputingthesetwoaspects13Simulation:Approaches„Thereare3primarysimulationapproacheszComputationalAeroacoustics(CAA)ŠSometimesreferredtoasDirectNoiseComputation(DNC)ŠSoundsourcesandpropagationsolvedinasinglecomprehensivemodelzSegregatedSource-PropagationMethods(SSPM)ŠSoundsourceandpropagationsolvedseparatelyviatwoseparatecomputationsfIntegralMethodsfBoundaryElementMethodsfVariationalMethodszStochasticNoiseGenerationandRadiation(SNGR)„WewilldiscusseachofthesemethodsindetailzTheoryzApplicabilityzAdvantages/DisadvantageszExamples14Outline„AeroacousticsBasics„SimulationMethodszComputationalAeroacoustics(CAA)zSegregatedSource-PropagationMethods(SSPM)ŠFundamentalsŠVariationalMethodsŠBoundaryElementMethodsŠIntegralMethodszStochasticNoiseGenerationandRadiation(SNGR)„Summary„Bibliography„SimulationGuide15CAA:Theory„CAA=ComputationalAeroAcousticsŠCAA::AeroacousticsŠDNS::TurbulencezDirectsimulation;nomodelsinvolved„PremisezFluidflowatsoundsourceandsoundpropagation,botharefluidphenomenaŠThereforebotharegovernedbyNavier-StokesequationszSolvetransientN-SequationstocalculatebothŠSoundgenerationŠPropagationfDomainspansfromsourcestoreceiverszMoststraightforwardintermsofbothimplementationandusageŠAcomprehensiveCFDcodesuchasFLUENTsolvestheNavier-StokesequationsŠSimplyconductatransientCFDsolutionandmeasurestaticpressureatmikeasfunctionoftime16CAA:TheorySoundSourceReceiverp’(t)PropagationComputationalDomain17PracticalproblemsinusingCAA„1]Frequencyrange(20Hz~20,000Hz)zAcoustictimescalesareoftenordersofmagnitudegreaterthanturbulencetimescaleszSimulationneedstoberunforlongrealtimewithasmalltimesteps,i.e.forlargeno.oftimesteps„2]RadiationtoFarFieldzDomainneedstoextendfromsourcetoreceiverzLargemeshsizesforfar-fieldsoundproblemse.g.aircraftnoiseheardonthegroundCAA:Applicability18„3]AcousticPressureMagnitudezMagnitudeoftheacousticpressureismuchlessthanthehydrodynamicpressurezNecessitatesuseofveryhighorderdiscreti