Fluent对旋转式动力机械的分析(ppt 164页).ppt

,IntroductiontoRotatingMachineryAnalysisUsingFluent,FrankKelecyFluentInc.,Agenda,IntroductionSinglemovingreferenceframe(SRF)modelMultiplemovingreferenceframe(MRF)modelMixingplanemodelSlidingmeshmodelQuestions?,Motivation,FlowsinvolvingrotatingdomainsoccurfrequentlyinengineeringExamplescompressorsandturbinesfansandpumpsrotatingcavities,seals,andbearingsmixingequipmentfluidcouplingdevicesandtorqueconvertersairmotorsmarineandaircraftpropellersandmanymoreComputationalFluidDynamics(CFD)todayplaysacentralroleinthedesignandanalysisofrotatingmachinery,ExamplesofRotatingMachinery,gasturbineengine,automotivewaterpump,tubeaxialfan,steamturbine,HVACblowerunit,hydroturbine,GoalsoftheTraining,ProvideanintroductiontorotatingmachinerymodelingExaminethefourmajorclassesofrotatingmachineryproblemsSinglerotatingreferenceframe(SRF)Multiplerotatingreferenceframe(MRF)MixingplaneSlidingmeshPresentdetailsonmodelingrotatingmachineryproblemsusingFluentModelsetupSolutionprocess(steady-stateandunsteady)Answeryourquestions!,TypesofRotatingMachinery,Inthiscourse,wewillclassifyrotatingmachineryasfollows:Turbomachinery-machineswhichaddworktoorextractworkfromafluidcompressors,fans,pumps-addworktoachieveapressureriseinthefluidturbines,windmills-extractworkfromfluidtodriveothermachinesMixingequipment-machineswhicharedesignedtomixfluid(andpossiblysolid)materialsforuseinachemicalprocessingapplicationindustrialmixingtanksRotatingtanks,seals,cavities,andotherdevicesdiskcavitiesandlabyrinthsealsingasturbineengineselectricmotorcoolingpassagesdiskdrivesrotatingtiresonautomotivevehiclesAlloftheseapplicationsinvolverotatingsurfacesanddomains(andthusmayusearotatingreferenceframeformodeling),ClassificationofTurbomachinery,AxialmachinesFlowthroughthemachineis(ingeneral)alignedwiththeaxisofrotationExamples:propellers,axialfans/compressors/turbines,swirlersCentrifugalmachinesFlowthroughthemachineis(ingeneral)perpendiculartotheaxisofrotationExamples:liquidpumps,centrifugalfans/compressors,radialturbinesMixedFlowFlowthroughthemachineissomewherebetweenaxialandcentrifugalExample:mixedflowcompressor,BasicProblemStatement,Wewishtosolvefortheflowthroughadomainwhichcontainsrotatingcomponentspropeller,compressor/turbineblade,radialimpeller,etc.stationaryand/orrotatingsurfacesductswalls,boresandcavities,sealteethsurfaces,etc.Rotation(s)assumedtobesteadyacceleratingreferenceframescanbemodeledwithsourceterms(notconsideredhere)Well-posedboundaryconditionsflowrates,pressures,temperatures,otherscalarsatinlet/outletboundarieswallmotion,thermal,otherBCsatwallsOtherconsiderationslaminar/turbulentflow,otherphysics(e.g.multiphaseflow,heattransfer)levelofinteractionbetweenmoving/stationarycomponents,ModelingApproaches,SingleRotatingFrame(SRF)EntirecomputationaldomainisreferredtorotatingreferenceframeMultipleRotatingFrame(MRF)SelectedregionsofthedomainarereferredtorotatingreferenceframesIgnoreinteractioneffectssteady-stateMixingPlane(MPM)Influenceofneighboringregionsaccountedforthroughuseofamixingplanemodelatrotating/stationarydomaininterfacesIgnorecircumferentialnon-uniformitiesintheflowsteady-stateSlidingMesh(SMM)MotionofspecificregionsaccountedforbymeshmotionalgorithmFlowvariablesinterpolatedacrossaslidinginterfaceUnsteadyproblem-cancaptureallinteractioneffectswithcompletefidelity,SingleReferenceFrame(SRF)Modeling,IntroductiontotheSRFModel,Manyproblemswhichinvolverotatingcomponentscanbemodeledusingasinglerotatingreferenceframe.Whyusearotatingreferenceframe?FlowfieldwhichisunsteadyinthestationaryframebecomessteadyintherotatingframeSteady-stateproblemsareeasiertosolve.simplerBCslowcomputationalcosteasiertopost-processandanalyzeWewilldiscussissuesrelatedtoSRFmodelinginthissection,butmanyconcepts(e.g.solversettings,physicalmodels,etc.)willalsoapplytoMRF,mixingplane,andslidingmeshmodeling.,IllustrationofSRFmodel,blade,hub,domain,rotatingreferenceframe,axis,shroud/casing,ImplicationsofSRF,SinglefluiddomainDomainrotateswithaconstantrotationalspeedaboutaspecifiedrotationalaxisEntiredomainmoveswiththereferenceframeBoundarieswhichmovewiththefluiddomainmayassumeanyshapeBoundarieswhicharestationary(withrespecttothelaboratoryorfixedframe)mustbesurfacesofrevolutionCanemployrotationally-periodicboundariesforefficiency(reduceddomainsize),StationaryWallsinSRFModels,stationarywall,rotor,baffle,Correct,Wrong!,Wallwithbafflesnotasurfaceofrevolution!,N-SEquations:RotatingReferenceFrame,TwodifferentformulationsareusedinFluentRelativeVelocityFormulation(RVF)ObtainedbytransformingthestationaryframeN-SequationstoarotatingreferenceframeUsestherelativevelocityasthedependentvariableinthemomentumequationsUsestherelativetotalinternalenergyasthedependentvariableintheenergyequationAbsoluteVelocityFormulation(AVF)DerivedfromtherelativevelocityformulationUsestheabsolutevelocityasthedependentvariableinthemomentumequationsUsestheabsolutetotalinternalenergyasthedependentvariableintheenergyequation,ReferenceFrames,x,y,z,z,y,x,stationaryframe,rotatingframe,axisofrotation,CFDdomain,AssumptionsNotranslation()Steadyrotation(w=constant)aboutspecifiedaxisaxispassesthroughoriginofrotatingframeIgnorebodyforcesduetogravityandothereffectsIgnoreenergysourcesDefinitionsAbsolutevelocity()-Fluidvelocitywithrespecttothestationary(absolute)referenceframeRelativevelocity()-Fluidvelocitywithrespecttotherotatingreferenceframe3-Dcompressible,laminarformsoftheequationspresentedinthefollowingslides,AssumptionsandDefinitions,TheVelocityTriangle,TherelationshipbetweentheabsoluteandrelativevelocitiesisgivenbyInturbomachinery,thisrelationshipcanbeillustratedusingthelawsofvectoraddition.ThisisknownastheVelocityTriangle,RelativeVelocityFormulation,(continuity),(xmomentum),(ymomentum),(zmomentum),(energy),RelativeVelocityFormulation(2),(relativevelocityvector),(relativetotalinternalenergy),(FouriersLaw),(viscousterms),RelativeVelocityFormulation(3),Accelerationtermsduetorotatingreferenceframe,Coriolisacceleration,centripetalacceleration,AbsoluteVelocityFormulation,(continuity),(xmomentum),(ymomentum),(zmomentum),(energy),AbsoluteVelocityFormulation(2),(absolutevelocityvector),(totalinternalenergy),(FouriersLaw),(viscousterms),AbsoluteVelocityFormulation(3),Accelerationtermduetorotatingreferenceframe,Accelerationreducestosingleterminvolvingrotationalspeedandabsolutevelocity,SRFGeometries:2-D,2-DProblems2-Dplanargeometriesrotateaboutaxisnormaltox-yplanewithspecifiedorigin(periodicboundariesarepermitted)2-Daxisymmetricgeometriesrotateaboutthex-axis,Planar,Axisymmetric,x,y,x,SRFGeometries:3-D,3-DProblemsUserdefinesbothrotationalaxisoriginanddirectionforthefluiddomainPeriodicboundariespermitted,origin,rotationalaxis,ChoiceofSolver,SameconsiderationsforgeneralflowfieldmodelingapplytoSRFsolverchoiceSegregatedSolver:incompressible,lowspeedcompressibleflowsExamples:Fans,blowers,pumpsCoupledSolvers:highspeedcompressibleflows,aboveMach0.3Examples:highpressureaxialcompressors,turbines,turbochargersVelocityFormulationrecommendationsUseAVFwheninflowcomesfromastationarydomainUseRVFwithcloseddomains(allsurfacesaremoving)orifinflowcomesfromarotatingdomainNOTE:RVFonlyavailableinthesegregatedsolverInmanycases,eithercanbeusedsuccessfully,BoundaryConditionsandPhysicalModels,BasicBCsusedinSRFanalysisFluidBCInflowBCsPressureInletVelocityInletMassFlowInletOutflowBCsPressureOutletWallsPeriodicsPhysicalmodelsTurbulencemodelsDPMMultiphase,realgas,heattransfer,FluidBCs,UsefluidBCpaneltoselectrotationalaxisoriginanddirectionvectorforrotatingreferenceframeNote:alldirectionvectorsshouldbeunitvectorsbutFluentwillnormalizethemiftheyarentSelectMovingReferenceFrameastheMotionTypeforSRFEnterrotationalspeedTranslationvelocitysettozero,VelocityInlets,Usedforincompressible,mildlycompressibleflowswheninletvelocityisknownCanspecifyabsoluteorrelativevelocityvectorCanspecifyvectorcomponentsinCartesianorcylindricalcoordinatesFor2-D,axisymmetricwithswirland3-Dproblemsyoucanspecifytangentialvelocityas,PressureInlets(1),Pressureinletscanbeusedwitheitherincompressibleorcompressibleflows.Definitionoftotalpressuredependsonvelocityformulationandcompressibility:,incompressible,AVF,incompressible,RVF,compressible,AVF,PressureInlets(2),SpecifyappropriatetotalpressureandtotaltemperatureIfinletflowissupersonic,specifystaticpressuresuchthatdesiredMachnumbercorrespondstopt/pSpecifyflowdirectionvectorCanuseCartesian,cylindrical,orlocalcylindricalcoordinatesystemFrameofflowdirectiondependsonvelocityformulation!Youcannotuseaframeofreferenceforthedirectionwhichisdifferentfromthevelocityformulation,MassFlowInlets,PrescribetotalmassflowrateormassfluxandtotaltemperatureforcompressibleflowsTotalpressure“floats”sincethemassflowrateisfixedPermitsflowdirectionspecificationinabsoluteframeonlyFluent6permitsdirectionspecificationinCartesianandcylindricalcoordinates,PressureOutlets,SpecifystaticpressureattheoutletCanemployaradialequilibriumassumptionwhichcomputesaradialpressurevariationfromThespecifiedpressureisthenassumedtobethehubstaticpressure,Backflow,BackflowoccurswhenthestaticpressureinacelladjacenttoapressureboundaryfallsbelowtheprescribedboundarypressureForSRFproblems,thedirectionofthebackflowisnormaltotheboundaryintheabsoluteframeifAVFisusednormaltotheboundaryintherelativeframeifRVFisusedRecommendationAssomebackflowmayoccurduringthesolutionprocess,prescribereasonablevaluesforallbackflowquantitiesTrytominimize(oreliminate)backflowbyextendingyouroutletboundaryfurtherdownstream,WallBCs,WallBCsenforcezeronormalvelocityatallwallsurfacesnoslip(zerovelocity)forviscousflowsFormovingreferenceframes,youcanspecifythewallmotionineithertheabsoluteorrelativeframesRecommendedspecificationofwallBCsforallmovingreferenceframeproblemsForstationarysurfaces(inthelabframe)usezeroRotationalspeed,AbsoluteFormovingsurfaces,usezeroRotationalspeed,RelativetoAdjacentCellZone,PeriodicBCs,RotationalperiodicBCsrelyontherotationalaxisspecificationtotransferinformationcorrectlyRotationallyperiodicboundariescanbeusedinSRFproblemstoreducemeshsizeprovidedboththegeometryandflowareperiodicNotes:Ifyouareusingthemake-periodiccommandintheTUI,makesureyousettherotationalaxisintheFluidBCpanelfirstbeforecreatingtheperiodicsOncetheperiodicBCshavebeenset,performagridchecktoseeifthereportedperiodicanglesarecorrect,TurbulenceModelsforRotatingMachinery,DPMModeling,YoucanuseDPMandpathlinemodelsforSRFproblemsParticlepathsarecomputedintherelativeframeIfyouwanttoseeparticlepathsintheabsoluteframe,youcanaccessthefollowingswitchintheTUI:define/models/dpm/tracking/track-in-absolute-frameNotethatparticlesmovinginabsoluteframemayhitwallsurfaces,sincetherotationoftheframeisnotaccountedfor,particleinjectionatbladetips,OtherModels,MultiphaseModelsVOF,ASMM,Eulerian(Fluent6)multiphasemodelsareallcompatiblewithSRFmodelinginFluentExamples:mixingtanks,multiphasepumpsflowsRealGasModelCanmodelspecificfluidsusingnon-idealgasequationofstateEmploystheREFPROPlibraryfromNISTForusewiththecoupled-solversonly!Availablefluidsinclude:carbondioxide,ammonia,butane,ethane,propane,propylene,widerangeofrefrigerants(e.g.R11,R12,R134a,etc.)HeatTransferConductionandradiationmodelscanbeenabledwithSRFmodelsNote:Forconductingsolidswhicharecontainedinamovingreferenceframe,youdontneedtoactivatetheMovingReferenceFrameoption!,SolverSettings(1),SegregatedsolverPressure-VelocityCouplingMethodSIMPLEissufficientformostproblemsUsePISOforunsteadyproblems(e.g.slidingmesh)PressureInterpolationStandardschemeisacceptableforlowspeedflows,butforhighlyswirlingflows.usePRESTO!ifyouhaveaquadorhexmeshuseBodyForceWeightedschemeformixedmeshesOtherequations-usesecondorderdiscretizationsCanstartwithfirstorderforstability,especiallyforproblemswithhighrotationalspeeds,SolverSettings(2),CoupledsolversUsefirstorderdiscretizationstobeginyourcalculation-thenswitchtosecondorderwhenthesolutionisclosetoconvergenceUsedefaultCourantnumbersasastart(1forexplicitsolver,5forimplicitsolver)Forcoupled-explicitsolverUse4levelsofFASmultigridformostproblemshelpspropagatesolutionmorerapidlythroughthedomainUsemorelevelsofyouhaveaverylargemesh,ExampleSRFCalculations,TwoexampleswillnowbepresentedtoillustratetypicalSRFmodelingprocedures:2-Dswirlingflowthroughadiskcavity3-Dflowthroughapropellerfan,DiskCavity,DiskcavityairflowstudybasedontheexperimentsofPincombe,1981Diskgeometry:radius(b)=443mm,width=59mm,bore=44.3mmSolutionsobtainedforfollowingconditions:Cw=Q/nb=1092,Ref=wb2/n=105Threedifferentnumericalconfigurationswereexamined:Case1-Stationaryframe,movingwallsCase2-SRF,RVFCase3-SRF,AVFAllcasesusedthesamemesh(20576quadcells),2Dsegregatedsolver(axisymmetricwithswirl),incompressibleflow,RKEturbulencemodel,secondorderdiscretizations,DiskCavity-Mesh,bothwallsrotate,inlet,outlet,axis,inlettube,DiskCavity-StreamFunction,Case1,Case2,Case3,separatedflow,Nearlyidenticalflowpatternsobservedforallthreecases.,RadialVelocityProfile(r/b=0.633),RadialVelocityProfile(r/b=0.833),DiskCavity-Results,ForceresultsConclusionsAllthreenumericalapproachesyieldessentiallythesameresultsDemonstratetheequivalenceofstationary,AVF,RVFapproaches,PropellerFan,3-DmodelofafourbladepropellerfanResultscomparedwithdatafromopenliterature:Oh,K-JandKang,S-H“Anumericalinvestigationofthedualperformancecharacteristicsofasmallpropellerfanusingviscousflowcalculations”ComputersandFluids28(1999)pp.815-823Solutionsobtainedforarangeofflowratesat2000rpmNumericalmodelMeshsize=269265cells(tets+wedges)SegregatedSolverwithmovingreferenceframeIncompressibleflow(air)Realizablek-emodelwithnon-equilibriumwallfunctions,PropellerFan-Mesh,ComparisontoData:HeadCoefficient,ComparisontoData:PowerCoefficient,FanFlowfield:FlowCoefficient=0.1,Significantflowreversalupstreamoffanface,Staticpressurecontoursdisplayedonfansurfaces,FanFlowfield:FlowCoefficient=0.35,Strongradialoutflow,FanFlowfield:FlowCoefficient=0.5,Strongaxialoutflow,SRFAppendix,AdditionalExamples2-Daxisymmetricflowinalabyrinthseal3-Dflowinatransonicaxialcompressorbladerow,LabyrinthSeal,2DaxisymmetricmodeloffivetoothlabyrinthsealResultscomparedwithexperimentaldataofMilwardandEdwards(ASME94-GT-56)Numericalmodelsteady-state,incompressibleflow2Daxisymmetric,withswirlandviscousdissipationsegregatedsolverRNGKEturbulencemodelmeshadaptionusedtoresolvetemperaturegradientssolutionscalculatedoverrangeofrotationalspeeds(2500-13000rpm),LabyrinthSeal-Mesh,adaptedcells,LabyrinthSeal-TotalTemperature,TotalTemperature(2),windageheatingduetoviscousdissipation,ComparisonwithData,TransonicAxialCompressor,Transoniccompressorrotor(NASARotor37)36bladesDesignconditions17188rpm,PR=2.1,massflow=20.2kg/sNumericalmodelsteady-state,compressibleflowcoupledimplicitsolvermesh:90,000hexcellsstandardKEturbulencemodel(inletTU=3.5%)inletprofilesfromtestdatabackpressurevariedtoobtainspeedline,Rotor37-Mesh,ComparisonwithData-PressureRatio,Chokedmassflowpredicted:20.80kg/sdata:20.93kg/s,PressureRatio-ChokedFlow,RelativeMachNo.-ChokedFlow,PressureRatio-94.3%RelativeMassflow,RelativeMachNo.-94.3%RelativeMassflow,MultipleReferenceFrame(MRF)Modeling,Introduction,Manyrotatingmachineryproblemsinvolvestationarycomponentswhichcannotbedescribedbysurfacesofrevolution(SRFnotvalid)SystemslikethesewhichinvolvebothstationaryandrotatingcomponentscanbeaddressedwithFluentusingthreedifferentapproachesMultiplereferenceframemodel(MRF)Mixingplanemodel(MPM)Slidingmeshmodel(SMM)TheMRFapproachisthesimplestandperhapsthemostapproximateofthethreeapproaches,WhatistheMRFModel?,Thedomainisdividedintostationaryandrotatingsubdomains.Morethanonerotatingsubdomainispermitted,andthesudomainscanrotateatdifferentspeeds.Attheinterfacesbetweentherotatingandstationarydomains,appropriatetransformationsofthevelocityvectorandvelocitygradientsareperformedtocomputefluxesofmass,momentum,energy,andotherscalarsNoaccountistakenforthe(assumed)relativemotionofonedomainwithrespecttotheotherForthisreasonMRFisoftenreferredtoasthe“frozenrotor”approach,ImplicationsoftheMRFModel,MultiplefluiddomainsRotatingsubdomainsmovewithprescribedrotationalspeedsassumesteadyrotationWallswhicharecontainedwithintherotatingsubdomaininterfacesareassumedtobemovingwiththefluidandmayassumeanyshapeTheinterfacebetweenarotatingsubdomainandtheadjacentstationarysubdomainmustbeasurfaceofrevolutionwithrespecttotheaxisofrotationoftherotatingsubdomainCanemployrotationallyperiodicboundaries,buttheperiodicanglesofallsubdomainsmustbeequal,IllustrationofInterfaceRulesforMRF,Correct,Wrong!,Interfaceisnotasurfaceorrevolution,stationarysubdomain,rotatingsubdomain,LimitationsoftheMRFModel,MRFmodelsignoretherelativemotionsofthesubdomainswitheachother,andthusdonotaccountforfluiddynamicinteractionbetweenstationaryandrotatingcomponentsIdeally,theflowattheMRFinterfacesshouldberelativelyuniformor“mixedout”MRFcanproducemisleadingresultsincaseswheretheflowpassesacrosstherotatingdomain(flowentersandleavestheouterboundaryoftherotatingdomain)Example:crossflowfansForthesecases,youshouldusetheslidingmeshmodel,SettingUpMRFProblems,GeneratemeshwithappropriatestationaryandrotatingfluidzonesInterfacescanbeconformalornon-conformalIfperiodicboundariesareused,performagridchecktoverifythatallsubdomainperiodicanglesareequalForeachrotatingfluidzone(FluidBC),selectMovingReferenceFrameastheMotionTypeandentertherotationalspeedSetallotherBCsandphysicalmodelsasusual(refertoSRFnotesmoremoreinformation)SolverrecommendationsaresameasSRFmodelsMayneedtolowerunderrelaxationfactorsiflargestartuppseudo-transientsarepresent(e.g.duetorotor-statorproximity),Non-conformalInterfaces,Whyusenon-conformalinterfacesforMRFproblems?PermitsmoremeshflexibilitythanconformalmeshesCaneasilyswitchfromMRFtoslidingmeshbychangingtheMotionTypeintheFluidBCfromMovingReferenceFrametoMovingMeshTosetupanon-conformalinterfaceSpecifyinterfacezonestobeoftypeInterfaceinBCpanelSelectzonepairsinGridInterfacespanelandclickonCreateEnablePeriodicoptionifinterfacesareadjacenttoperiodiczones,IllustrationofNon-conformalInterface,Non-conformalinterface,ExampleMRFCalculations,SeveralexampleswillnowbepresentedtoillustratetypicalMRFmodelingprocedures:Squirrelc