fluent用户手册摘要.docx

fluent用户手册摘要.docx

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fluent用户手册摘要

Tomakethemostappropriatechoiceofmodelforyourapplication,youneedtounderstandthecapabilitiesandlimitationsofthevariousoptions.Duetothestronginteractionofthemeanflowandturbulence,thenumericalresultfortheturbulentflowstendtobemoresusceptibletomeshdependencythanthoseforlaminarflows.Recommendedthatresolve,withsufficientlyfinemeshes,regionswherethemeanflowundergoesrapidchangesandtheshearwithlargestrainrates.Checkthenear-wallmeshbydisplayingorplottingywhichisavailableinthepostprocessingdialogboxes.

Fluent后处理

1，建模及网格生成：

gambit或者分离的CAD系统产生几何结构模型机网格；也可用Tgrid从已有的面网格中产生体网格；也可以从相关CAD软件包生成体网格，然后读入Tgrid或者fluent。

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。

TheRNGturbulencemodelinANSYSFLUENThasanoptionofusingadifferentialformulafortheeffectiveviscosityµefftoaccountforthelow-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