湍流及气动噪声仿真培训

ANSYSCFD湍流模型及流动噪声高级应用培训姓名刘伟公司安世亚太目录•ANSYSCFD湍流模型新发展•ANSYSCFD湍流模型使用技巧•ANSYSCFD湍流模型验证案例•ANSYSCFD流动噪声模型简介•ANSYSCFD噪声计算案例主题•ANSYSCFD湍流模型新发展•ANSYSCFD湍流模型使用技巧•ANSYSCFD湍流模型验证案例•ANSYSCFD流动噪声模型简介•ANSYSCFD噪声计算案例TurbulenceModelsinFLUENTIncreaseincomputationalcostOne-EquationModelSpalart-AllmarasTwo-EquationModelsStandardk–εRNGk–εRealizablek–εStandardk–ωSSTk–ωk-kl-ωTransitionModel(3eq.)SSTTransitionModel(4eq.)4-Equationv2fModelReynoldsStressModelDetachedEddySimulationSASLargeEddySimulationRANSModelsMenter’sSSTk-ωModel•Thetwosetsofequationsandthemodelconstantsareblendedinsuchawaythattheresultingequationsettransitionssmoothlyfromoneequationtoanother.()∂∂∂∂===−202222*141110,12max4,500,maxminargargtanhjjkkxxkCDyCDkyykFωωρσσρωνωβωωωω()()γσσβφφφφρρω,,,where112111outer1inner1kFFDtDkFDtDkF=−+=⋅⋅⋅+−+⋅⋅⋅+layeroutlertheinlayerinnerthein0111→=FFWilcox’originalk-ωmodelεε23k=Wallk-ωmodeltransformedfromstd.k-εmodelModifiedWilcoxk-ωmodelEmbeddedLES•嵌入式大涡模拟–也可以和DES/SAS模型联用E-LES:FullydevelopedchannelflowViscosityratiooniso-surfacesofq-criterion(-500)MeanvelocityvaluesinsideLESzone.RANSLESRe=395E-LES:Spatiallydecayingturbulence•AlargenumberofturbulencemodelsareavailableinCFX,somehaveveryspecificapplicationswhileotherscanbeappliedtoawiderclassofflowswithareasonabledegreeofconfidenceRANSEddy-viscosityModels:1)ZeroEquationmodel.2)SAmodel3)Standardk-εmodel.4)RNGk-εmodel.5)Standardk-ωmodel.6)Baseline(BSL)zonalk-ωbasedmodel.7)SSTzonalk-ωbasedmodel.8)(k-ε)1Emodel.RANSReynolds-StressModels:1)LRRReynoldsStress2)QIReynoldsStress3)Speziale,SarkarandGatskiReynoldsStress4)SMC-ωmodel5)Baseline(BSL)Reynolds'StressmodelEddySimulationModels:1)LargeEddySimulation(LES)[transient]2)DetachedEddySimulation(DES)*[transient]3)ScaleAdaptiveSimulationSST(SAS)*[transient]*NotavailableintheANSYSCFD-FloproductTurbulenceModelsinCFXTransitionModellinginIndustrialCFD•Renumbereffects•Heattransfer•Wallshearstress•Separationbehaviour•EfficiencyofmanytechnicaldevicesEffectsModelling•Numerousdevelopments:–Correlationbasedmodels–Low-Remodels–enlinearstability–…–DNSAlmostallindustrialCFDsimulationsarecalculatedwithoutatransitionmodelTransitionModellinginIndustrialCFD•Low-Remodels(onlybypasstransition)–Basedontransportequationsfore.g.kandε(compatiblewithmodernCFDcodes)–Cannotbecalibratedindependentlyofviscoussublayermodel–Pooraccuracyandrobustness–notusedinindustry•eNmethod(onlynaturaltransition)–Veryaccuratepredictionsfor2Dairfoils(lowFSTI)–N-Scodesarenotaccurateenoughtoevaluatestabilityequations–Extensiontogeneric3Dflowsverydifficult(impossible?)–Cannotaccountofnon-lineareffects(e.g.highFSTI,roughness)•Correlationbasedmodel–Reasonablyaccurate–Correlationscanbefoundformanydifferenttransitionmechanisms(e.g.FSTI,dp/dx,Roughness)–Notcompatiblewith3Dflowsandunstructured/parallelCFDcodes–non-localformulationGoal–correlationbasedmodelusingtransportequationsTransitionModelFormulationinCFX•2TransportEquations–Intermittency(γ)Equation•Fractionofturbulentvslaminarflow•TransitiononsetcontrolledbyrelationbetweenvorticityReynoldsnumberandReθt–TransitionOnsetReynoldsnumberEquation•Usedtopassinformationaboutfreestreamconditionsintob.l.e.g.impingingwakesUnsteadyModels•URANS–URANSgivesunphysicalsinglemodeunsteadybehavior•LES(LargeEddySimulation)–Tooexpensiveformostindustrialflowsduetohighresolutionrequirementsinboundarylayers•DES(DetachedEddySimulation)–Firstindustrial-strengthmodelforhigh-RewithLES-content–Increasedcomplexity(gridsensitivity)duetoexplicitmixoftomodellingconcepts•SAS(Scale-AdaptiveSimulation)–ExtendsURANStomanytechnicalflows–Provides“LES”-contentinunsteadyregions.URANSSAS-URANSHybridModels•HybridModel:–RANSequationsinbl–LES„detached“regions•Switchofmodel–Basedonratioofturbulentlength-scaletogridsize–DifferentnumericaltreatmentinRANSandLESregionsRANSLES?∆≤cLt∆≥cLt•OvercomesthresholdlimitofLES•StronggridsensitivityinRANSregion•OpenquestionconcerningtransitionregionbetweenRANSandLES主题•ANSYSCFD湍流模型新发展•ANSYSCFD湍流模型使用技巧•ANSYSCFD湍流模型验证案例•ANSYSCFD流动噪声模型简介•ANSYSCFD噪声计算案例IndustrialTurbulentFlowsthinshearflowsrotating&swirlingflowscrossflow/secondaryflowsrapidlystrainedflowstransitionalflowsseparated&recirculatingflowslarge-scaleunsteadinessthickBL,mildlyseparatedflowsthinshearflowsrotating&swirlingflowsrapidlystrainedflowstransitionalflowsseparated&recirculatingflowslarge-scaleunsteadinessthickBL,mildlyseparatedflows如何选择合适的湍流模型？IstheFlowTurbulent?ExternalFlowsInternalFlowsNaturalConvectionalongasurfacearoundanobstaclewherewhereOtherfactorssuchasfree-streamturbulence,surfaceconditions,blowing,suction,andotherdisturbancesetc.maycausetransitiontoturbulenceatlowerReynoldsnumbers(Rayleighnumber)etc.,,,hddxL=(Prandtlnumber)ReynoldsNumberEffectsRe3.5×1063×105Re3.5×10640Re150150Re3×1055-15Re40Re5Turbulentvortexstreet,buttheseparationisnarrowerthanthelaminarcaseBoundarylayertransitiontoturbulentLaminarboundarylayeruptotheseparationpoint,turbulentwakeLaminarvortexstreetApairofstablevorticesinthewakeCreepingflow(noseparation)ChoicestobeMadeTurbulence