best practices for turbulent heat transfer

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1、BestPracticesforTurbulentHeatTransferPepiMaksimovicFluentInc.AUTOUGM2003Confidential1Outline•Review–EnergyEquation–TurbulenceModeling–BuoyancyInducedFlows•ExampleTestCases–1–TurbulentPipeFlow–2–2DBackstep–3–NaturalConvectionfromaCylinderAUTOUGM2003Confidential2Outline•ExampleTestCases(co

2、nt’d)–4–BluntPlate–5–TurbineBlade–6–ImpingingJet•SummaryofLessonsLearnedAUTOUGM2003Confidential3EnergyEquation:Introduction•Energytransportequation:∂()ρE+∇⋅()V()ρE+p=∇⋅keff∇T−∑hjJj+(τeff⋅V)+Sh∂tjConductionSpeciesdiffusionViscousdissipation•EnergyEdefinedas:2pvE=h−+ρ2AUTOUGM2003Co

3、nfidential4TurbulentHeatTransfer•TheReynoldsaveragingoftheenergyequationproducesanadditionalterm,wheretheinstantaneoustemperatureisT=T+t′AUTOUGM2003Confidential5TurbulentHeatTransfer–AnalogoustotheReynoldsstresses,thisistheturbulentheatfluxterm.Anisotropicturbulentdiffusivityisassumed:kT

4、whereυ=TρCpTurbulentdiffusivityisusuallyrelatedtoeddyviscosityviaaturbulentPrandtlnumber(modifiablebytheusers)AUTOUGM2003Confidential6IstheFlowTurbulent?ExternalFlowsρULwhereReL≡5µRe≥5×10alongasurfacexL=x,D,D,etc.hRe≥20,000aroundanobstacleDOtherfactorssuchasfree-streamturbulence,surfacec

5、onditions,andInternalFlowsdisturbancesmaycauseearliertransitiontoturbulentflow.Re≥2,300DhNaturalConvectionwhereistheRayleighnumberAUTOUGM2003Confidential7TurbulenceModelsinFluentZero-EquationModelsOne-EquationModelsRANS-basedSpalart-AllmarasmodelsTwo-EquationModelsStandardk-εRNGk-εIncrea

6、seinRealizablek-εComputationalCostStandardk-ωPerIterationSSTk-ωAvailableV2FModelinFLUENT6.1Reynolds-StressModelDetachedEddySimulationLarge-EddySimulationDirectNumericalSimulationAUTOUGM2003Confidential8WallBoundaryConditions•Accuratenear-wallmodelingisimportant:–Successfulpredictionoffri

7、ctionaldrag,pressuredrop,separation,etc.,dependsonthefidelityoflocalwallshearpredictions.–Near-wallmodelingisusedtosupplyboundaryconditionsforturbulentflows.AUTOUGM2003Confidential9WallBoundaryConditions•Mostk-εandRSMturbulencemodelsarenotvalidinthenear-wallregion:u+y+–Sp