ANSYS 12.0 官方培训手册-Introduction to CFX-PART B and C.ppt

ANSYS12.0TrainingManualCFX12.0,IntroductiontoCFXPartBChapter4-6,96Pages,Chapter4SolverSettings,IntroductiontoCFX,Overview,InitializationSolverControlOutputControlSolverManager,Note:Thischapterconsiderssolversettingsforsteady-statesimulations.Settingsspecifictotransientsimulationarediscussedinalaterchapter.,IterativesolutionproceduresrequirethatallsolutionvariablesareassignedinitialvaluesbeforecalculatingasolutionAgoodinitialguesscanreducethesolutiontimeInsomecasesapoorinitialguessmaycausethesolvertofailduringthefirstfewiterationsTheinitialvaluescanbesetin3ways:SolverautomaticallycalculatestheinitialvaluesInitialvaluesareenteredbytheuserInitialvaluesareobtainedfromaprevioussolutionInitialvaluescanbesetonaper-domainbasisorgloballyforalldomains,Initialization,InitializationSettingInitialValues,InsertGlobalInitialisationfromthetoolbarorbyright-clickingonFlowAnalysis1EditeachDomaintosetinitialvaluesonaper-domainbasisWhenbotharedefinedthedomainsettingstakeprecedenceSoliddomainmusthaveinitialconditionssetonaper-domainbasis,InitializationSettingInitialValues,TheAutomaticoptionmeansthattheCFX-SolverwillcalculateaninitialvalueforthesolvedvariableunlessapreviousresultsfileisprovidedWillbebasedonboundaryconditionvaluesanddomainsettingsTheAutomaticwithValueoptionmeansthatthespecifiedvaluewillbeusedunlessapreviousresultsfileisprovidedCanuseaconstantvalueoranexpression,InitializationUsingaPreviousSolution,TouseaprevioussolutionastheinitialguessenabletheInitialValuesSpecificationtogglewhenlaunchingtheSolverYoucanprovidemultipleinitialvaluesfilesWhensimulatingasystemyoucanprovideprevioussolutionsforeachcomponentofthesystemastheinitialguessUsuallyeachfilewouldcorrespondtoaseparateregionofspaceItisbestifdomainsintheSolverInputFiledonotoverlapwithmultipleinitialvaluesfiles,EdittheSolverControlobjectintheOutlinetree,SolverControlEditing,TheSolverControlpanelcontainsvariouscontrolsthatinfluencethebehaviorofthesolverThesecontrolsareimportantfortheaccuracyofthesolution,thestabilityofthesolverandthelengthoftimeittakestoobtainasolution,SolverControlOptions,SolverControlAdvectionScheme,TheAdvectionSchemereferstothewaytheadvectionterminthetransportequationsismodelednumericallyi.e.thetermthataccountsforbulkfluidmotionOftenthedominanttermThreeschemesareavailable,HighResolution,UpwindandSpecifiedBlendDiscussedinmoredetailnextThereisrarelyanyreasontochangefromthedefaultHighResolutionscheme,SolverControlAdvectionSchemeTheory,Solutiondataisstoredatnodes,butvariablevaluesarerequiredatthecontrolvolumefacestocalculatefluxesTheupstreamnodalvalues(fup)areinterpolatedtotheintegrationpoints(fip)onthecontrolvolumefacesusing:WhereisthevariablegradientandisthevectorbetweentheupstreamnodeandtheintegrationpointInotherwords,theipvalueisequaltotheupstreamvalueplusacorrectionduetothegradientbcanhavevaluesbetween0and1,SolverControlAdvectionSchemeTheory,Ifb=0wegettheUpwindadvectionscheme,i.e.nocorrectionThisisrobustbutonlyfirstorderaccurateSometimesusefulforinitialruns,butusuallynotnecessaryTheSpecifiedBlendschemeallowsyoutospecifybbetween0and1(i.e.betweennocorrectionuptofullcorrection)Butthisisnotguaranteedtobebounded,meaningthatwhenthecorrectionisincludeditcanovershootorundershootwhatisphysicallypossibleTheHighResolutionschememaximizesbthroughouttheflowdomainwhilekeepingthesolutionbounded,Theory,HighResolutionScheme,UpwindScheme,=1.00,Flowismisalignedwithmesh,0,1,SolverControlTurbulenceNumerics,RegardlessoftheAdvectionSchemeselection,theTurbulenceequationsdefaulttotheFirstOrder(Upwind)schemeUsuallythisissufficientTheHighResolutionschemecanbeselectedforadditionalaccuracyCangivebetteraccuracyinboundarylayersonunstructuredmeshes,SolverControlConvergenceControl,TheSolverwillfinishwhenitreachesMax.IterationsunlessconvergenceisachievedsoonerIfMax.IterationsisreachedyoumaynothaveaconvergedsolutionCanbeusefultosetMax.IterationstoalargenumberWhentheSolverfinishesyoushouldalwayscheckwhyitfinishedFluidTimescaleControlsetsthetimescaleinasteady-statesimulation,ANSYSCFXemploysthesocalledFalseTransientAlgorithmAtimescaleisusedtomovethesolutiontowardsthefinalanswerInasteady-statesimulationthetimescaleprovidesrelaxationoftheequationnon-linearitiesAsteady-statesimulationisa“transient”evolutionoftheflowfromtheinitialguesstothesteady-stateconditionsConvergedsolutionisindependentofthetimescaleused,InitialGuess,50iterations,100iterations,150iterations,FinalSolution,SolverControlTimescaleBackground,Forobtainingsuccessfulconvergence,theselectionofthetimescaleplaysanimportantroleIfthetimescaleistoolarge,theconvergencebecomesbouncyormayevenleadtothefailureoftheSolverIfthetimescaleistoosmall,theconvergencewillbeveryslowandthesolutionmaynotbefullyaccurate,SolverControlTimescaleSelection,SolverControlTimescaleSelection,Foradvectiondominatedflow,afractionofthefluidresidencetimeisoftenagoodestimateforthetimescaleAtimescaleof1/3of(LengthScale/VelocityScale)isoftenoptimalMayneedasmallertimescaleforthefirstfewiterationsandforcomplexphysics,transonicflow,.Forrotatingmachines,1/(inrad/s)isagoodchoiceForbuoyancydrivenflows,thetimescaleshouldbebasedonafunctionofgravity,thermalexpansivity,temperaturedifferenceandlengthscale(seedocumentation),TimescaleControlcanbeAutoTimescale,PhysicalTimescaleorLocalTimescaleFactorPhysicalTimescaleSpecifythetimescale.UsuallyaconstantbutcanalsobevariableviaanexpressionCanoftensetabettertimescalethanAutoTimescalewouldproducefasterconvergence,SolverControlTimescaleControl,SolverControlTimescaleControl,AutoTimescaleTheSolvercalculatesatimescalebasedonboundary/initialconditionsorcurrentsolutionanddomainlengthscaleUseaConservativeorAggressiveestimateforthedomainlengthscale,oraspecifiedvalueTimescaleisre-calculatedandupdatedeveryfewiterationsastheflowfieldchangesCansetaMaximumTimescaletoprovideanupperlimitTendstoproduceaconservativetimescaleTimescalefactor(default=1)isamultiplierwhichcanbechangedtoadjusttheautomaticallycalculatedtimescale,LocalTimescaleFactorTimescalevariesthroughoutthedomainCanaccelerateconvergencewhenvastlydifferentlocalvelocityscalesexistE.g.ajetenteringaplenumBestusedonfairlyuniformmeshes,sincesmallelementwillhaveasmalltimescalewhichcanslowconvergenceLocalTimescaleFactorisamultiplierofthelocaltimescaleNeveruseasfinalsolution;alwaysfinishoffwithaconstanttimescale,LocalTimescale=,LocalMeshLengthScaleLocalVelocityScale,SmallerTimescaleinhighvelocityand/orfinemeshregions,SolverControlTimescaleControl,SolverControlConvergenceCriteria,ConvergenceCriteriasettingsdeterminewhenthesolutionisconsideredconvergedandhencewhentheSolverwillstopAssumingMax.IterationsisnotreachedResidualsareameasureofhowaccuratelythesetofequationshavebeensolvedSinceweareiteratingtowardsasolution,wenevergettheexactsolutiontotheequationsLowerresidualsmeanamoreaccuratesolutiontothesetofequations(moreonthenextslide)Donotconfuseaccuratelysolvingtheequationswithoverallsolutionaccuracytheequationsmayormaynotbeagoodrepresentationofthetruesystem!Residualsarejustonemeasureofaccuracyandshouldbecombinedwithothermeasures:MonitorPoints(ch.8)andImbalances(below),Thecontinuousgoverningequationsarediscretizedintoasetoflinearequationsthatcanbesolved.Thesetoflinearequationscanbewrittenintheform:A=bwhereAisthecoefficientmatrixandisthesolutionvariableIftheequationweresolvedexactlywewouldhave:A-b=0TheresidualvectorRistheerrorinthenumericalsolution:A-b=RSinceeachcontrolvolumehasaresidualweusuallylookattheRMSaverageorthemaximumnormalizedresidual,SolverControlResidualsTheory,ResidualTypeMAX:ConvergencebasedonmaximumresidualanywhereRMS:ConvergencebasedonaverageresidualfromallcontrolvolumesRootMeanSquare=ResidualTargetForreasonableconvergenceMAXresidualsshouldbe1.0E-3,RMSshouldbeatleast1.0E-4ThetargetsdependentontheaccuracyneededLowervaluesmaybeneededforgreateraccuracy,SolverControlResiduals,SolverControlConservationTarget,TheConservationTargetsetsatargetfortheglobalimbalancesTheimbalancesmeasuretheoverallconservationofaquantity(mass,momentum,energy)intheentireflowdomain,ClearlyinaconvergedsolutionFluxInshouldequalFluxOutItsgoodpracticetosetaConservationTargetand/ormonitortheimbalancesduringtherunWhenset,theSolvermustmeetboththeResidualandConservationTargetbeforestopping(assumingMax.Iterationsisnotreached)Setatargetof0.01(1%)orlessFluxInFluxOut=0.5istrue,SolverControlElapsedTimeandInterruptControl,ExamplesIftemperatureexceedsaspecifiedvalueif(areaAve(T)wall200C,1,0)IfmeshqualitydropsbelowaspecifiedvalueinamovingmeshcaseMoreonlogicalexpressionsintheCELlecture,ThisoptionisonlyavailablewhenasoliddomainisincludedinthesimulationTheSolidTimescaleshouldbeselectedsuchthatitisMUCHlargerthanthefluidtimescale(100timeslargeristypical)theenergyequationisusuallyverystableinthesolidzonesolidtimescalesaretypicallymuchlargerthanfluidtimescales,SolverControlSolidTimescaleControl,ThefluidtimescaleisestimatedusingLengthScale/VelocityScaleThesolidtimescaleisautomaticallycalculatedasfunctionofthelengthscale,thermalconductivity,densityandspecificheatcapacityOryoucanchoosethePhysicalTimescaleoptionandprovideatimescaledirectly,TheEquationClassSettingstabisanadvancedoptionthatcanbeusedtosetSolvercontrolsonanequationspecificbasisNotusuallyneededWilloverridethecontrolssetonBasicSettingsfortheselectedequationAdvancedOptionsAdvancedsolvercontroloptionsRarelyneeded,SolverControlEquationClassSettings,OutputControlsResults,TheOutputControlsettingscontroltheoutputproducedbytheSolverTheTrnResults,TrnStatsandExporttabonlyapplytotransientsimulationsandarecoveredintheTransientchapterTheResultstabcontrolsthefinal.resfileGenerallydonotusetheSelectedVariables(orNone!)optionsinceitprobablywontcontainenoughinformationtorestarttherunlaterOutputEquationResidualsisusefulifyouneedtocheckwhereconvergenceproblemsareoccurringExtraOutputVariablesListcontainsvariablesthatarenotwrittentothestandardresultsfileE.g.Vorticity,Frequencyofoutputcanbeadjusted,OutputControlsBackup,TheBackuptabcontrolsifandwhenbackupresultsfilesareautomaticallywrittenbytheSolverRecommendforlongSolverrunsincaseofpowerfailure,networkinterruptions,etcOption:Standard:LikeafullresultsfileEssential:AllowsacleansolverrestartSmallest:Canrestartthesolver,buttherellbeajumpintheresidualsSelectedVariables:NotrecommendedCanalsomanuallyrequestabackupfilefromtheSolverManageratanytime,TheMonitortaballowsyoutocreateMonitorPointsTheseareusedtotrackvaluesofinterestastheSolverrunsTheCartesianCoordinatesOptionisusedtotrackthevalueofavariableataspecificX,Y,ZlocationTheExpressionOptionisusedtomonitorthevaluesofaCELexpressionE.g.CalculatetheareaaverageofCpattheinletboundary:areaAve(Cp)inletE.g.Massflowofparticularfluidthroughanoutlet:oil.massFlow()outletInsteady-statesimulationsyoushouldcreatemonitorpointsforquantitiesofinterestOnemeasureofconvergenceiswhenthesevaluesarenolongerchanging,OutputControlsMonitor,TheCFX-SolverManagerisagraphicaluserinterfaceusedto:DefinearunControltheCFX-SolverinteractivelyViewinformationabouttheemergingsolutionExportdata,SolverManager,DefineanewSolverrunSolverInputFileshouldbethe.deffileCanalsopick.res,.bakor_full.trnfilestorestartapreviousincompleterunTomakeaphysicschangeandrestartasolution,createanew.deffileandprovideitastheSolverInputFilethenselectthe.res,.bakor_full.trnfileintheInitialValuesSpecificationsectionIfbothfileshavethesamephysics,thisisthesameaspickingthe.res/.bak/_full.trnfileastheinputfileUseMeshFromselectswhichmeshtouse.Ifthemeshesareidenticalcanuseeitheroption,otherwise:IfyouusetheSolverInputFilemesh,theInitialValuessolutionisinterpolatedontotheinputfileIfyouusetheInitialValuesmeshonlythephysicsfromtheSolverInputFileisusedContinueHistoryFromcarriersoverconvergencehistoryanditerationcounters,SolverManagerDefiningaRun,SolverManagerDefiningaParallelRun,BydefaulttheSolverwillruninserialAsinglesolverprocessrunsonthelocalmachineSettheRunModetooneoftheparalleloptionstomakeuseofmultiplecores/processorsRequiresparallellicensesAllowsyoutodividealargeCFDproblemintosmallerpartitionsFastersolutiontimesSolvelargerproblemsbymakinguseofmemory(RAM)onmultiplemachinesTheLocalParalleloptionsshouldbeusedwhenrunningonasinglemachineTheDistributedParalleloptionsshouldbeusedwhenrunningacrossmultiplemachines,SerialLocalParallelDistributedParallelDifferentcommunicationmethodsareavailable(MPICH2,HPMPI,PVM)Seedocumentation“WhenToUseMPIorPVM”formoredetails,butHPMPIisrecommendedinmostcases,SolverManagerDefiningaParallelRun,TheShowAdvancedControltoggleenablesthePartitioner,SolverandInterpolatortabsOnthePartitionertabyoucanpickdifferentpartitioningalgorithmsPartitioningisalwaysaserialprocessCanbeaproblemforv.largecasessinceyoucannotdistributethememoryloadacrossmultiplemachinesThedefaultMeTiSalgorithmusesmorememorythanothers,soifyourunoutofmemoryuseadifferentmethod(seedocumentationfordetails)MultidomainOption:IndependentPartitioning:EachdomainispartitionedintonpartitionsCoupledPartitioning:AlldomainsarecombinedandthenpartitionedintonpartitionsTheresaspecificoptionforTransientRotorStatorcases,SolverManagerDefineRunAdvancedControls,OntheSolvertabyoucanselecttheDoublePrecisionoptionThesolverwillusemoresignificantfiguresinitscalculationsDoublessolvermemoryrequirementsUsewhenround-offerrorcouldbeaproblemifsmallvariationsinavariableareimportant,wheresmallisrelativetotheglobalrangeofthatvariable,e.g:ManyMeshMotioncases,sincethemotionisoftensmallrelativetothesizeofthedomainMostCHTcases,sincethermalconductivityisvastlydifferentinthefluidandsolidIfyouhaveawidepressurerange,butsmallpressurechangesareimportantSmallvaluesbythemselvesdonotneedDP,SolverManagerDefineRunAdvancedControls,TheSolverestimatesitsmemoryrequirementsupfrontMemoryAllocFactorisamultiplierforthisestimateUsewhenthesolverstopswithan“InsufficientMemoryAllocated”error,SolverManagerInteractiveSolverControl,DuringasolutionEditRuninProgressletsyoumakechangesontheflyModelsgenerallycannotbechanged,buttimescales,BCs,etccan,.outfile,MonitorPlot,SolverManagerAdditionalSolutionMonitors,Right-click,BydefaultmonitorplotsarecreatedshowingtheRMSresidualsforeachequationsolved,plusoneplotforanymonitorpointsRight-clicktoswitchbetweenRMSandMAXAdditionalmonitorscanbeselectedshowing:ImbalancesBoundaryfluxes(FLOW)BoundaryforcesTangential(viscous)Normal(pressure)Sourceterms,NewMonitor,StartanewSimulation,MonitorRuninProgress,MonitorFinishedRun,StopCurrentRun,SaveCurrentRun,SwitchResidualPlotbetweenRMSandMAX,Bydraggingthecursoroveranyicon,thefeaturedescriptionwillappear,SolverManagerAdditionalIcons,Chapter5CFDPost,IntroductiontoCFX,CFD-Postisaflexible,state-of-the-artpost-processorforANSYSCFDproducts(CFXandFLUENT)Itcanrunasastandalonepost-processor,orwithinWorkbenchIncludesalltheexpectedplottingobjectsPlanes,Isosurfaces,Vectors,Streamlines,Contours,Animations,Allowsprecisequantitativeanalysis:Weightedaverages,forces,FFT,resultscomparison,built-inanduserdefinedmacros,Cancreateuserdefinedscalar/vectorvariablesIncludesAutomaticReports,Charts(XY,Time,Histograms),Tables,SupportsSessionfiles,Statefiles,CommandandExpressionLanguages(includingthePerlprogramminglanguage),Overview,WithintheCFX-SolverManagerFromtheCFXLauncherWithinANSYSWorkbenchFromtheStartMenuorCommandLineStartProgramsANSYS12.0ANSYSCFD-Post,HowToStartCFD-Post,GUILayout,Outlinetab(“modeltree”),Detailsview,Additionaltabs(varioustools),VariousViewers(3D,Chart,),PreparelocationswheredatawillbeextractedfromorplotsgeneratedCreatevariables/expressionswhichwillbeusedtoextractdata(ifnecessary)i)Generatequalitativedataatlocationsii)GeneratequantitativedataatlocationsGenerateReports,CFD-PostGeneralWorkflow,CreatingLocations,LocationsarecreatedfromtheInsertmenuorfromthetoolbarOncecreated,allLocationsappearasentriesintheOutlinetree,UsethecheckboxesnexttoeachobjectintheOutlinetreetoquicklycontrolvisibility,Double-clickobjectsintheOutlinetreetoedit,Right-clickobjectsintheOutlinetreetoDuplicateorDelete,CreatingLocations,Domain,Subdomain,BoundaryandMeshRegionsarealwaysavailableBoundaryandMeshRegionscanbeeditedandcolouredbyanyvariableMeshRegionsprovidesallavailableinterior/exterior2D/3DregionsfromthemeshAllLocationsyoucreatearelistedunderUserLocationsandPlotsAllitemscontainedintheReportarelistedhere,PlanesXYPlane,PointandNormal,etc.Candefineacircleorrectangletoboundtheplane,otherwiseitsboundedonlybythesolutiondomain(s)PointXYZ:Atcoordinates.CanpickfromViewerNodeNumber:SomesolvererrormessagesgiveanodenumberVariableMax/Min:Usefultolocatewheremax/minvaluesoccurPointCloudCreatemultiplepointsUsuallyusedasseedstostreamlines,vectors,LocationTypes,LocationTypes,LinesStraightlinebetweentwopointsUsuallyusedasthebasisforanXYChartPolylinesAlsousedforChartsReadpointsfromafileUsethelineofintersectionbetweenaboundaryandanotherlocationExtractalinefromacontourplot,LocationTypes,VolumesElementsareeitherinoroutNocutvolumesFromSurfaceAvolumeisformedfromallelementstouching(orabove/below)theselectedlocationCanbeusefulformeshcheckingIsovolumeBaseonavariableat,aboveorbelowagivenvalue,orbetweentwovalues,LocationTypes,IsosurfacesSurfaceofavariableataspecifiedvalueIsoClipAnIsoCliptakesacopyofanyexistinglocationandthenclipsitusingoneormorecriteriaE.g.aoutletboundaryplotwhichisthenclippedbyVelocity=10m/sandVelocityNewinthetophalfoftheVariablestabThereare3methodsforUserDefinedvariablesTheExpressionmethoddefinesavariableviaanexpression,whichcanbeafunctionofanyothervariableUsuallycreatetheexpressionfirstontheExpressionstab.Exampleonnextslide.FrozenCopyhasbeensupersededbyCaseComparisonTheGradientmethodcalculatesthegradientofanyexistingscalarvariableProducesanewvectorvariable,Goal:PlotanisosurfaceatVelRatio=0.7where,OntheExpressionstabcreatetheexpressionforVelocityRatio:OntheVariablestabcreateanewvariablenamedVelRatiousingMethod=Expression,UserDefinedVariablesExample,CreateanIsosurfaceusingthevariableVelRatioatavalueof0.7,UserDefinedVariablesExample,Goal:PlotanisosurfaceatVelRatio=0.7where,ExpressionsTab,TheExpressionstabshowsallexistingexpressionsandallowsyoutocreatenewexpressionsRight-clickinthetopareaNe