fluent中多孔介质设置问题和算例

经过难过的一段经历，终于将局部问题实情大白，为了使保位同仁不再经过我之难过，此刻将自己多孔介质经验宣告以下，希望各位能加精：1。Gambit中区分网格以后，定义需要做为多孔介质的地区为fluid,与缺省的fluid分别开来，再定义其名称，我习惯将名称定义为porous;2。在

fluent

中定义界限条件

define-boundarycondition-porous(

刚定义的名称

)，将其设置界限条件为

fluid,

点击

set

按钮即弹出与

fluid

界限条件相同的对话框，选中

porouszone

与

laminar

复选框,再点击

porouszone

标签即出现一个带有转动条的界面；3。porouszone设置方法：1）定义矢量：二维定义一个矢量，第二个矢量方向不用定义，是与第一个矢量方向正交的；三维定义二个矢量，第三个矢量方向不用定义，是与第一、二个矢量方向正交的；（如何知道矢量的方向：翻开grid图，看看X,Y,Z的方向，假如是X向，矢量为1,0,0,同理Y向为0,1,0，Z向为0,0,1,假如所需要的方向与坐标轴正向相反，则定义矢量为负）圆锥坐标与球坐标请参照fluent帮助。2）定义粘性阻力1/a与内部阻力C2：请参看自己上一篇博文“终于搞清fluent中多孔粘性阻力与内部阻力的计算方法”，此处不赘述；3）假如了定义粘性阻力1/a与内部阻力C2,就不用定义C1与C0，由于这是两种不一样的定义方法，C1与C0只在幂率模型中出现，该处保持默认就行了；4）定义孔隙率porousity，默认值1表示全开放，此值按实验测值填写即可。完了，其余设置与一般k-e或RSM相同。总结一下，与君共享!Tutorial7.ModelingFlowThroughPorousMediaIntroductionManyindustrialapplicationsinvolvethemodelingofflowthroughporousmedia,suchasfilters,catalystbeds,andpacking.Thistutorialillustrateshowtosetupandsolveaprobleminvolvinggasflowthroughporousmedia.Theindustrialproblemsolvedhereinvolvesgasflowthroughacatalyticconverter.Catalyticconvertersarecommonlyusedtopurifyemissionsfromgasolineanddieselenginesbyconvertingenvironmentallyhazardousexhaustemissionstoacceptablesubstances.Examplesofsuchemissionsincludecarbonmonoxide(CO),nitrogenoxides(NOx),andunburnedhydrocarbonfuels.Theseexhaustgasemissionsareforcedthroughasubstrate,whichisaceramicstructurecoatedwithametalcatalystsuchasplatinumorpalladium.Thenatureoftheexhaustgasflowisaveryimportantfactorindeterminingtheperformanceofthecatalyticconverter.Ofparticularimportanceisthepressuregradientandvelocitydistributionthroughthesubstrate.HenceCFDanalysisisusedtodesignefficientcatalyticconverters:bymodelingtheexhaustgasflow,thepressuredropandtheuniformityofflowthroughthesubstratecanbedetermined.Inthistutorial,FLUENTisusedtomodeltheflowofnitrogengasthroughacatalyticconvertergeometry,sothattheflowfieldstructuremaybeanalyzed.Thistutorialdemonstrateshowtodothefollowing:_Setupaporouszoneforthesubstratewithappropriateresistances._Calculateasolutionforgasflowthroughthecatalyticconverterusingthepressurebasedsolver._Plotpressureandvelocitydistributiononspecifiedplanesofthegeometry._Determinethepressuredropthroughthesubstrateandthedegreeofnon-uniformityofflowthroughcrosssectionsofthegeometryusingX-Yplotsandnumericalreports.ProblemDescriptionThecatalyticconvertermodeledhereisshowninFigure.Thenitrogenflowsinthroughtheinletwithauniformvelocityofm/s,passesthroughaceramicmonolithsubstratewithsquareshapedchannels,andthenexitsthroughtheoutlet.Whiletheflowintheinletandoutletsectionsisturbulent,theflowthroughthesubstrateislaminarandischaracterizedbyinertialandviscouslosscoefficientsintheflow(X)direction.Thesubstrateisimpermeableinotherdirections,whichismodeledusinglosscoefficientswhosevaluesarethreeordersofmagnitudehigherthanintheXdirection.SetupandSolutionStep1:GridReadthemeshfile(catalytic.File/Read/Case...Checkthegrid.Grid/CheckFLUENTwillperformvariouschecksonthemeshandreporttheprogressintheconsole.Makesurethattheminimumvolumereportedisapositivenumber.3.Scalethegrid.Grid!Scale...SelectmmfromtheGridWasCreatedIndrop-downlist.ClicktheChangeLengthUnitsbutton.Alldimensionswillnowbeshowninmillimeters.ClickScaleandclosetheScaleGridpanel.4.Displaythemesh.Display/Grid...(a)Makesurethatinlet,outlet,substrate-wall,andwallareselectedintheSurfacesselectionlist.ClickDisplay.RotatetheviewandzoomintogetthedisplayshowninFigure.ClosetheGridDisplaypanel.Thehexmeshonthegeometrycontainsatotalof34,580cells.Step2:Models2.Selectthestandardk-εturbulencemodel.Define/Models/Viscous...Step3:Materials1.AddnitrogentothelistoffluidmaterialsbycopyingitfromtheFluentDatabaseformaterials.Define/Materials...(a)ClicktheFluentDatabase...buttontoopentheFluentDatabaseMaterialspanel.i.Selectnitrogen(n2)fromthelistofFluentFluidMaterials.ii.ClickCopytocopytheinformationfornitrogentoyourlistoffluidmaterials.ClosetheFluentDatabaseMaterialspanel.(b)ClosetheMaterialspanel.Step4:BoundaryConditions.Define/BoundaryConditions...1.Settheboundaryconditionsforthefluid(fluid).SelectnitrogenfromtheMaterialNamedrop-downlist.ClickOKtoclosetheFluidpanel.2.Settheboundaryconditionsforthesubstrate(substrate).SelectnitrogenfromtheMaterialNamedrop-downlist.EnablethePorousZoneoptiontoactivatetheporouszonemodel.EnabletheLaminarZoneoptiontosolvetheflowintheporouszonewithoutturbulence.ClickthePorousZonetab.i.Makesurethattheprincipaldirectionvectorsaresetasshownin.Usethescrollbartoaccessthefieldsthatarenotinitiallyvisibleinthepanel.ii.EnterthevaluesinTablefortheViscousResistanceandInertialResistance.Scrolldowntoaccessthefieldsthatarenotinitiallyvisibleinthepanel.(e)ClickOKtoclosetheFluidpanel.3.Setthevelocityandturbulenceboundaryconditionsattheinlet(inlet).(a)Enterm/sfortheVelocityMagnitude.(b)SelectIntensityandHydraulicDiameterfromtheSpecificationMethoddropdownlistintheTurbulencegroupbox.Retainthedefaultvalueof10%fortheTurbulentIntensity.Enter42mmfortheHydraulicDiameter.ClickOKtoclosetheVelocityInletpanel.4.Settheboundaryconditionsattheoutlet(outlet).(a)Retainthedefaultsettingof0forGaugePressure.(b)SelectIntensityandHydraulicDiameterfromtheSpecificationMethoddropdownlistintheTurbulencegroupbox.Enter5%fortheBackflowTurbulentIntensity.Enter42mmfortheBackflowHydraulicDiameter.ClickOKtoclosethePressureOutletpanel.Retainthedefaultboundaryconditionsforthewalls(substrate-wallandwall)andclosetheBoundaryConditionspanel.Step5:Solution(a)RetainthedefaultsettingsforUnder-RelaxationFactors.(b)SelectSecondOrderUpwindfromtheMomentumdrop-downlistintheDiscretizationgroupbox.(c)ClickOKtoclosetheSolutionControlspanel.EnablePlotintheOptionsgroupbox.ClickOKtoclosetheResidualMonitorspanel.Enabletheplottingofthemassflowrateattheoutlet.Solve/Monitors/Surface...(a)SettheSurfaceMonitorsto1.(b)EnablethePlotandWriteoptionsformonitor-1,andclicktheDefine...buttontoopentheDefineSurfaceMonitorpanel.i.SelectMassFlowRatefromtheReportTypedrop-downlist.SelectoutletfromtheSurfacesselectionlist.ClickOKtoclosetheDefineSurfaceMonitorspanel.(c)ClickOKtoclosetheSurfaceMonitorspanel.4.Initializethesolutionfromtheinlet.Solve/Initialize/Initialize...SelectinletfromtheComputeFromdrop-downlist.ClickInitandclosetheSolutionInitializationpanel.5.Savethecasefile(catalytic.File/Write/Case...6.Runthecalculationbyrequesting100iterations.Solve/Iterate...Enter100fortheNumberofIterations.ClickIterate.TheFLUENTcalculationwillconvergeinapproximately70iterations.Bythispointthemassflowratemonitorhasattendedout,asseeninFigure.(c)ClosetheIteratepanel.7.Savethecaseanddatafiles(catalyticandcatalytic.File/Write/Case&Data...Note:Ifyouchooseafilenamethatalreadyexistsinthecurrentfolder,FLUENTwillpromptyouforconfirmationtooverwritethefile.Step6:Post-processingCreateasurfacepassingthroughthecenterlineforpost-processingpurposes.Surface/Iso-Surface...SelectGrid...andY-CoordinatefromtheSurfaceofConstantdrop-downlists.ClickComputetocalculatetheMinandMaxvalues.Retainthedefaultvalueof0fortheIso-Values.Entery=0fortheNewSurfaceName.ClickCreate.Createcross-sectionalsurfacesatlocationsoneithersideofthesubstrate,aswellasatitscenter.Surface/Iso-Surface...SelectGrid...andX-CoordinatefromtheSurfaceofConstantdrop-downlists.ClickComputetocalculatetheMinandMaxvalues.Enter95forIso-Values.Enterx=95fortheNewSurfaceName.ClickCreate.Inasimilarmanner,createsurfacesnamedx=130andx=165withIso-Valuesof130and165,respectively.ClosetheIso-Surfacepanelafterallthesurfacesbeencreated.

haveCreatealinesurfaceforthecenterlineoftheporousmedia.Surface/Line/Rake...(a)EnterthecoordinatesofthelineunderEndPoints,usingthestartingcoordinateof(95,0,0)andanendingcoordinateof(165,0,0),asshown.Enterporous-clfortheNewSurfaceName.ClickCreatetocreatethesurface.ClosetheLine/RakeSurfacepanel.4.Displaythetwowallzones(substrate-wallandwall).Display/Grid...DisabletheEdgesoption.EnabletheFacesoption.DeselectinletandoutletinthelistunderSurfaces,andmakesurethatonlysubstrate-wallandwallareselected.ClickDisplayandclosetheGridDisplaypanel.EnabletheLightsOnoptionintheLightingAttributesgroupbox.RetainthedefaultselectionofGourandintheLightingdrop-downlist.ClickApplyandclosetheDisplayOptionspanel.Setthetransparencyparameterforthewallzones(substrate-wallandwall).Display/Scene...Selectsubstrate-wallandwallintheNamesselectionlist.ClicktheDisplay...buttonunderGeometryAttributestoopentheDisplayPropertiespanel.i.SettheTransparencysliderto70.ii.ClickApplyandclosetheDisplayPropertiespanel.ClickApplyandthenclosetheSceneDescriptionpanel.7.Displayvelocityvectorsonthey=0surface.Display/Vectors...(a)EnabletheDrawGridoption.TheGridDisplaypanelwillopen.i.Makesurethatsubstrate-wallandwallareselectedinthelistunderSurfaces.ClickDisplayandclosetheDisplayGridpanel.(b)Enter5fortheScale.(c)SetSkipto1.(d)Selecty=0fromtheSurfacesselectionlist.(e)ClickDisplayandclosetheVectorspanel.Theflowpatternshowsthattheflowentersthecatalyticconverterasajet,withrecirculationoneithersideofthejet.Asitpassesthroughtheporoussubstrate,itdeceleratesandstraightensout,andexhibitsamoreuniformvelocitydistribution.Thisallowsthemetalcatalystpresentinthesubstratetobemoreeffective.Figure:VelocityVectorsonthey=0PlaneDisplayfilledcontoursofstaticpressureonthey=0plane.Display/Contours...EnabletheFilledoption.EnabletheDrawGridoptiontoopentheDisplayGridpanel.i.Makesurethatsubstrate-wallandwallareselectedinthelistunderSurfaces.ii.ClickDisplayandclosetheDisplayGridpanel.MakesurethatPressure...andStaticPressureareselectedfromtheContoursofdrop-downlists.Selecty=0fromtheSurfacesselectionlist.ClickDisplayandclosetheContourspanel.Figure:ContoursoftheStaticPressureonthey=0planeThepressurechangesrapidlyinthemiddlesection,wherethefluidvelocitychangesasitpassesthroughtheporoussubstrate.Thepressuredropcanbehigh,duetotheinertialandviscousresistanceoftheporousmedia.DeterminingthispressuredropisagoalofCFDanalysis.Inthenextstep,youwilllearnhowtoplotthepressuredropalongthecenterlineofthesubstrate.Plotthestaticpressureacrossthelinesurfaceporous-cl.Plot/XYPlot...(a)MakesurethatthePressure...andStaticFunctiondrop-downlists.

Pressure

areselected

fromtheYAxisSelectporous-clfromtheSurfacesselectionlist.ClickPlotandclosetheSolutionXYPlotpanel.Figure:PlotoftheStaticPressureontheporous-clLineSurfaceInFigure,thepressuredropacrosstheporoussubstratecanbeseentoberoughly300Pa.DisplayfilledcontoursofthevelocityintheXdirectiononthex=95,x=130andx=165surfaces.Display/Contours...DisabletheGlobalRangeoption.SelectVelocity...andXVelocityfromtheContoursofdrop-downlists.Selectx=130,x=165,andx=95fromtheSurfacesselectionlist,anddeselecty=0.(d)ClickDisplayandclosetheContourspanel.Thevelocityprofilebecomesmoreuniformasthefluidpassesthroughtheporousmedia.Thevelocityisveryhighatthecenter(theareainred)justbeforethenitrogenentersthesubstrateandthendecreasesasitpassesthroughandexitsthesubstrate.Theareaingreen,whichcorrespondstoamoderatevelocity,increasesinextent.Figure:ContoursoftheXVelocityonthex=95,x=130,andx=165SurfacesUsenumericalreportstodeterminetheaverage,minimum,andmaximumofthevelocitydistributionbeforeandaftertheporoussubstrate.Report/SurfaceIntegrals...SelectMass-WeightedAveragefromtheReportTypedrop-downlist.SelectVelocityandXVelocityfromtheFieldVariabledrop-downlists.Selectx=165andx=95fromtheSurfacesselectionlist.ClickCompute.(e)SelectFacetMinimumfromtheReportTypedrop-downlistandclick(f)SelectF