ANSYS FLUENT中的自然对流问题.pdf

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1、CustomerTrainingMaterialLt4Lecture4NaturalConvectionHeatTransferHeatTransferModelingusingANSYSFLUENTANSYSFLUENTANSYS,Inc.ProprietaryRelease13.0©2010ANSYS,Inc.Allrightsreserved.L4-1December2010HeatTransferModelingusingANSYSFLUENTOutlineCustomerTrainingMaterial1.Theory/Definition4.ModelsetupinFLUENTa.

2、Phenomenaa.Referencedensityandb.TransitionTransitiontoturbulentflowtoturbulentflowtemperatureb.Boussinesqvs.incompressibleidealgas2.Turbulencea.Dyyynamicvs.thermalboundary5.ElExampleslayera.Validationcase–Tallcavityb.Fullbuoyancyeffectb.Baselinecasesi.CCoseddoaloseddomainwithhighRayayegleigh3.MdliMo

3、delingtiipsnumbera.Pressurediscretizationii.PlumewithhighRayleighnumberb.Timesteppingforunsteadyc.Industrialcase–GlasstankTC21simulation6.References7.AppppendixANSYS,Inc.ProprietaryRelease13.0©2010ANSYS,Inc.Allrightsreserved.L4-2December2010CustomerTrainingMaterialNaturalconvection:Theory&Definition

4、s&DefinitionsANSYS,Inc.ProprietaryRelease13.0©2010ANSYS,Inc.Allrightsreserved.L4-3December2010HeatTransferModelingusingANSYSFLUENTPhenomenaCustomerTrainingMaterial•Innaturalconvection,fluid∂PmotionisgeneratedduetoP+dx∂xT=Tdidensittdydiffifference(b(buoyancy))iinwthefluidcausedbytemperature∂ττyxyxΓxτ

5、+dygradients.yx∂xy•BodyforcesT=Tf–TypicallygravitationalP–Centrifugal(rotatingmachinery)–Coriolis(atmosphericandoceanicvorticalmotion)•Forthisclassofproblems,flowForcesactingonafluidparticleinandenergyarestronglycoupled.naturalconvection.ANSYS,Inc.ProprietaryRelease13.0©2010ANSYS,Inc.Allrightsreserv

6、ed.L4-4December2010HeatTransferModelingusingANSYSFLUENTLaminartoTurbulentTransitionCustomerTrainingMaterial•Innaturalconvection,theReynoldsnumbernolongercharacterizestheflow.•Withanappropriatereferencevelocity,itispossibletodetermineacriticalvalueoftheRayleighnumber(Ra).L–Experimentsshowthatthecriti

7、calRayleighnumber,Ra,isaround109.c–ThetransitionzoneisquitelargeasRavariesbetween106and1010.BuoyancyforceKinematic3βgLΔTνviscosityRa=GrPr=wherPr=LLναeαKinematicviscosityKinematicviscosityThermaldiffus