fluent用户手册摘要Word下载.docx
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初始化的时间
注意:
fluent有一个格式转换器允许从其他程序读入结构网格。
计算花费
数值耗散
Createalineforplottingthecenterlinevelocitydistribution:
link/rakesurface---输入中心线的两点坐标,newsurfacename命名为centerline,---solutionXYplot,curve设置中心线格式---设置plotdirection为某一轴线,例如设置x轴为plotdirection,y轴为速度大小,surface选择中心线
Createalineforplottingthevelocityprofileattheoutlet.
有旋与旋转流动问题
有旋流动在一些燃烧器里用来增加流体滞留时间和驻涡,从而稳定燃烧。
Segregatedsolveronly:
对四边形和六面体网格,选用presto;
为求解大压力梯度和轴向速度梯度,网格必须足够精密;
三维有旋流动:
定义速度进口需要用柱坐标,求解时要渐渐增加旋转速度;
轴对称旋转,旋转轴必须是x轴,网格必须在y=0以上。
旋转流动中,边界层很薄,fluent需要在靠近旋转边界的地方网格比较细;
轴向速度比较陡,近中心线为典型的自由涡流动,因此为保证好的求解效果,网格要求比较密。
RNGk-_
Model
TheeffectofswirlonturbulenceisincludedintheRNGk-_
model,enhancingaccuracyforswirlingflows
RNGturbulencemodel,thedifferentialviscositymodel:
useadifferentialformulafortheeffectiveviscosityμefftoaccountforthelow-Reynolds-numbereffects
OnceyouchosetheRNGmodel,theswirlmodificationtakeseffect,bydefault,forall
three-dimensionalflowsandaxisymmetricflowswithswirl.Thedefaultswirlconstantissetto0.07,whichworkswellforweaklytomoderatelyswirlingflows.However,forstronglyswirlingflows,youmayneedtousealargerswirlconstant.
_sisaswirlconstantthatassumesdifferentvaluesdependingonwhethertheflowisswirl-dominatedoronlymildly温和的,和善的,适度的swirling.Thisswirlmodificationalwaystakeseffectforaxisymmetric,swirlingflowsandthree-dimensionalflowswhentheRNGmodelisselected.Formildlyswirlingflows_sissetto0.07.Forstronglyswirlingflows,however,ahighervalueof_scanbeused.
Differentialviscositymodel考虑边界层的低雷诺数的影响。
TheRNGturbulencemodelinANSYSFLUENThasanoptionofusingadifferentialformulafortheeffectiveviscosityµ
efftoaccountforthelow-Reynolds-numbereffects.
DifferentialViscosityModelspecifieswhetherornotthelow-Reynolds-numberRNGmodificationstoturbulentviscosityshouldbeincluded.Bydefault,thisoptionisturnedoff.Itislikelytohaveaneffectonlywhenthenear-wallregionsinthedomainarewellresolved已解决的intermsof依据,按照meshdensity.
SwirlDominatedFlowspecifieswhetherornottheRNGmodificationtoturbulentviscosityforswirlingflowsshouldbeincluded.Thisoptionisavailableonlyin3Dand2Daxisymmetricswirlsolvers,anditcanyieldimprovedpredictionswhensolvingflowswithsignificantswirl.
Thestandardwallfunctionsworkreasonablywellforabroadrangeofwallboundedflows.However,theytendtobecomelessreliablewhentheflowsituationsdepartfromtheidealconditionsthatareassumedintheirderivation.Amongothers,theconstant-shearandlocalequilibriumassumptionsaretheonesthatmostrestricttheuniversalityofthestandardwallfunctions.Accordingly,whenthenear-wallflowsaresubjectedto屈服,受制severepressuregradients,andwhentheflowsareinstrongnon-equilibrium,thequalityofthepredictionsislikelytobecompromised
Thenon-equilibriumwallfunctionsofferedasanadditionaloptionthatcanpotentiallyimprovetheresultsinsuchsituations。
Reattachment回帖,重附着,再附impingement冲击,碰撞viscoussublayer黏性底层identical一致的,相同的coarse粗糙的
StandardWallFunctionsvs.Non-EquilibriumWallFunctions
Becauseofthecapabilitytopartlyaccountfortheeffectsofpressuregradients,thenone-quilibriumwallfunctionsarerecommendedforuseincomplexflowsinvolvingseparation,reattachment,andimpingementwherethemeanflowandturbulencearesubjectedtopressuregradientsandrapidchanges.Insuchflows,improvementscanbeobtained,particularlyinthepredictionofwallshear(skin-frictioncoefficient)andheattransfer(NusseltorStantonnumber).
Fortriangularandtetrahedralmeshes,sincetheflowisneveralignedwiththemesh,youwillgenerallyobtainmoreaccurateresultsbyusingthesecond-orderdiscretization.Forquad/hexmeshes,youwillalsoobtainbetterresultsusingthesecond-orderdiscretization,especiallyforcomplexflows.
Whilethehigher-orderschememayresultingreateraccuracy,itcanalsoresultinconvergencedifficultiesandinstabilitiesatcertainflowconditions.Ontheotherhand,usingafirst-orderschememaynotprovidethedesiredaccuracy.Oneapproachtoachievingimprovedaccuracywhilemaintaininggoodstabilityistouseadiscretizationblendingfactor.Ablendingfactoroflessthan1(typically0.75or0.5)willmaketheconvectivefluxesmorediffusive,whichinsomeflowconditionscanstabilizeasolutionthatisotherwiseunstablewhenthefullhigher-order
discretizationschemeisemployed.Notethatinordertousethisfeatureeffectively,makesurethatoneoftheallowedhigherorderdiscretizationschemesisselectedforthedesired
variablesintheSolutionMethodstaskpage.
TheQUICKschemeisapplicabletoquadrilateralorhexahedralmeshes,IfQUICKisusedforhybridmeshes,itwillbeusedonlyforquadrilateralandhexahedralcells.Second-orderupwinddiscretizationwillbeappliedtoallothercells.
NotethatSIMPLE,SIMPLEC,PISO,andFractionalStepusethepressure-basedsegregatedalgorithm,whileCoupledusesthepressure-basedcoupledsolver.
TheSIMPLEalgorithmusesarelationshipbetweenvelocityandpressurecorrectionstoenforcemassconservationandtoobtainthepressurefield.
IfyouchooseSIMPLECunderPressure-VelocityCoupling,youmustalsosettheSkewness
Correction,whosedefaultvalueis0.
IfyouchooseCoupled,youwillhavetospecifytheCourantnumberintheSolutionControls
taskpage,whichissetat200bydefault.YouwillalsospecifytheExplicitRelaxation
FactorsforMomentumandPressure,whicharesetat0.75bydefault.
Ifhigh-ordermomentumdiscretizationisused,youmayneedtodecreasetheexplicit明确的,显式relaxationto0.5.Forcaseswithveryskewedmeshes,theruncanbestabilizedbyfurtherreductionoftheexplicitrelaxationfactorto0.25.
Itisgoodpracticetobeginacalculationusingthedefaultunder-relaxationfactors.Iftheresidualscontinuetoincreaseafterthefirst4or5iterations,youshouldreducetheunder-relaxationfactors.
Acautiousapproachistosaveadatafilebeforemakinganychangestotheunder-relaxationfactors,andtogivethesolutionalgorithmafewiterationstoadjusttothenewparameters.Typically,anincreaseintheunder-relaxationfactorsbringsaboutaslightincreaseintheresiduals,buttheseincreasesusuallydisappearasthesolutionprogresses.Iftheresidualsjumpbyafew
ordersofmagnitude,youshouldconsiderhaltingthecalculationandreturningtothelastgooddatafilesaved.
Formostflows,thedefaultunder-relaxationfactorsdonotusuallyrequiremodification.Ifunstableordivergentbehaviorisobserved,however,youneedtoreducetheunder-relaxationfactorsforpressure,momentum,k,andfromtheirdefaultvaluestoabout0.2,0.5,0.5,and0.5.(Itisusuallynotnecessarytoreducethepressureunder-relaxationforSIMPLEC.)Inproblemswheredensityisstronglycoupledwithtemperature,asinvery-high-Rayleigh-numbernatural-ormixed-convectionflows,itiswisetoalsounder-relaxthetemperatureequationand/ordensity(i.e.,useanunder-relaxationfactorlessthan1.0).Conversely,whentemperatureisnotcoupledwiththemomentumequations(orwhenitisweaklycoupled),asinflowswithconstantdensity,theunder-relaxationfactorfortemperaturecanbesetto1.0.
Forotherscalar标量,数量equationsthedefaultunder-relaxationmaybetooaggressiveforsomeproblems,especiallyatthestartofthecalculation.Youmaywishtoreducethefactorsto0.8tofacilitateconvergence.
Notethatwithoptimal最佳的,理想的,优化的settings,theconvergenceofthecoupledpressure-velocityalgo-rithmwillbelimitedbythesegregatedsolutionofotherscalarequations,e.g.,turbulence.Foroptimumsolverperformance,youwillneedtoincreasetherelaxationfactorsfortheseequationstoavaluegreaterthanthedefaultvalues.
herearetwomethodsforinitializingthesolution:
•Initializetheentireflowfield(inallcells).
•Patchvaluesorfunctionsforselectedflowvariablesinselectedcellzonesor“registers”ofcells.(Registersarecreatedwiththesamefunctionsthatareusedtomarkcellsforadaption.)
Beforepatchinginitialvaluesinselectedcells,youmustfirstinitializetheentireflowfield.Youcanthenpatchthenewvaluesovertheinitializedvaluesforselectedvariables.
Console控制台,主控台,;
安慰,慰藉;
graphics图形,图像integrate集成,结合,求积分manully手动的,用手。
Monitoringsurfaceintegralscanbeusedtocheckforbothiterationconvergenceandmesh
independence.Forexample,youcanmonitortheaveragevalueofacertainvariableon
asurface.Whenthisvaluestopschanging,youcanstopiterating.Youcanthenadapt
themeshandreconvergethesolution.Thesolutioncanbeconsideredmesh-independent
whentheaveragevalueonthesurfacestopschangingbetweenadaptions.
Formostproblems,thedefaultconvergencecriterioninANSYSFLUENTissufficient.
Thiscriterionrequiresthatthescaledresidualsdecreaseto10*-3forallequationsexcepttheenergyandP-1e