Ansys-12.0-CFX-官方教程-15A

15-1ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002598Chapter15ReviewandTipsIntroductiontoCFXReviewandTips15-2ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002598TrainingManualDomainInterfaces•DomainInterfacescanbeusedaspartofameshingstrategyaswellasforconnectingdifferentdomainsorreferenceframestogether•BoundaryconditionsarecreatedineachdomainwhenaDomainInterfaceiscreated;generallyyoushouldnoteditthesedirectly•WhenthemeshisdifferentoneachsideoftheinterfaceaGGI(GeneralGridInterface)isused–ThiswillusemorememoryintheSolverthanacontinuousmesh–AccuracyacrossaGGIinterfaceisusuallynotaconcernaslongasthemeshlengthscalesoneachsidearesimilar•AutomaticDomainInterfacesarecreatedbyCFX-Preinsomecases–Alwayschecktheseanddon’tassumethatalltherequiredDomainInterfaceshavebeencreatedReviewandTips15-3ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002598TrainingManualSources•Sourcesareusedtoaccountforphysicsorprocessesthathavenotbeendirectlyresolvedinthesimulation•Momentumsourcescanbeusedtocreateapressuredrop(e.g.ascreen,aporousmaterial)orapressurerise(e.g.afan)•Energysourcescanaccountforheatadded/removedfromthesimulation•Whensourcesarefunctionsofthesolvedvariable(e.g.momentumsourcesthatarefunctionsofvelocity,energysourcesthatarefunctionsoftemperature)theSourceCoefficientshouldbeset–TheSourceCoefficientmustbenegativeotherwisethesolverwilldiverge–Mayneedtore-writetheSourcesothatishasanegativederivative][10][400*]/[3000SourceEnergy3KTKmW][10]/[3000)(tCoefficienSourceEnergy3KmWTSourceReviewandTips15-4ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002598TrainingManualTransientSimulations•Inatransientanalysisthetimestepshouldbesmallenoughtocapturethetransientbehaviourofinterest•Boundaryconditionscanbefunctionsoftime•Convergenceshouldbemonitoredsothateachtimestepisconverged–Itisgenerallybettertoreducetheoveralltimestepsizetoimproveconvergenceratherthanincreasingthenumberofcoefficientloops•RemembertocreatetheTransientResultsobjectbeforerunningReviewandTips15-5ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002598TrainingManualTurbulence•EstimatetheflowReynoldsNumbertodetermineiftheflowislaminarorturbulent•Checky+valuestomakesurethenear-wallmeshissuitable–y+300foraWallFunctionsolution–y+=2withtheSSTmodelforalow-Resolution•TheSSTmodelisagoodchoiceforageneralturbulencemodel•Beawareofthelimitationsoftheturbulencemodelchosen–RANSmodelsresolvethemeanflowfield,thereforealotoftransientturbulentstructuresarenotcaptured•Thesemaybeimportantwhensimulatingnoiseandvibration–Thek-emodelcangiveinaccurateseparationpredictionsReviewandTips15-6ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002598TrainingManualHeatTransfer•Highspeedflows(Mach0.2)shouldusetheTotalEnergymodel•ThedoubleprecisionsettingfortheSolverisrecommendedforCHTsimulations(i.e.whenasoliddomainisincluded)•AlwaysmakesureenergyimbalanceshavereachedacceptablelevelsinCHTcases•EnableViscousWorkorViscousDissipationifheatingduetoviscouseffectsisimportant•Ifthermalradiationismodeledchooseanappropriatemodeldependingontheopticalthickness•ThinWallmodelingandthermalcontactresistancescanbesetatdomaininterfacesReviewandTips15-7ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002598TrainingManualMovingZones•Movingboundariescanbesimulatedinseveraldifferentways•Forrotatingwalls,awallvelocitycansimplybeimposedifthemotionispurelytangential(e.g.arotatinghuborasolidbrakedisk)•Whentherotatingwallshaveanormalcomponentofvelocitytheymustbeplacedinsidearotatingdomain(e.g.blades,ventedbrakedisk)–Stationarywallsthenbecomecounter-rotatingintherotatingdomainandmustformsurfacesofrevolution(i.e.nonormalcomponentofvelocity)–AlthoughaMeshMotionapproachispossible,itismuchmorecomputationallyexpensive•Meshmotionisusuallyusedtosimulatedeformingboundariesorlinear/cyclicmotionReviewandTips15-8ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002598TrainingManualMovingZones•Atachangeinreferenceframeaframechangemodelisused–Fromlowfidelity/costtohighfidelity/costthechoicesareFrozenRotor,StageorTransientRotorStator•Otherapproachesformovingregionsare:–RigidBodyMotion•A6-DOFsolvescalculatesthesolidbodymotion•UsedinconjunctionwithMeshMotion–ImmersedSolid•UsedtosimulatemovingsolidsthatcannotbeaccommodatedwithMeshMotionReviewandTips15-9ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002598TrainingManualWhyDoesMyCaseFailintheSolver?•Firstcarefullyreadtheerrormessage–TheerrormessagemayrecommendsettinganExpertParameter–Thismaybeanappropriatefix,oritmaymaskanunderlyingproblem•Example:+--------------------------------------------------------------------+|CheckingforIsolatedFluidRegions|+--------------------------------------------------------------------+2isolatedfluidregionswerefoundindomainR1……turnoffthischeckbysettingtheexpertparametercheckisolatedregions=f.•Thiserr