fluent中多孔介质设置问题和算例之欧阳育创编.docx

fluent中多孔介质设置问题和算例之欧阳育创编.docx

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fluent中多孔介质设置问题和算例之欧阳育创编

经过痛苦的一段经历，终于将局部问题真相大白，为了使保位同仁不再经过我之痛苦，现在将本人多孔介质经验公布如下，希望各位能加精：

时间：

2021.02.04

创作：

欧阳育

1。

Gambit中划分网格之后，定义需要做为多孔介质的区域为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中定义边界条件define-boundarycondition-porous（刚定义的名称），将其设置边界条件为fluid,点击set按钮即弹出与fluid边界条件一样的对话框，选中porouszone与laminar复选框,再点击porouszone标签即出现一个带有滚动条的界面；

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：

打开grid图，看看X,Y,Z的方向，如果是X向，矢量为1,0,0,同理Y向为0,1,0，Z向为0,0,1,如果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考fluent帮助。

2）定义粘性阻力1/a与内部阻力C2：

请参看本人上一篇博文“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）如果了定义粘性阻力1/a与内部阻力C2,就不用定义C1与C0，因为这是两种不同的定义方法，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，其他设置与普通k-e或RSM相同。

总结一下，与君共享!

Tutorial7.ModelingFlowThroughPorousMedia

Introduction

Manyindustrialapplicationsinvolvethemodelingofflowthroughporousmedia,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.

ProblemDescription

ThecatalyticconvertermodeledhereisshowninFigure7.1.Thenitrogenflowsinthroughtheinletwithauniformvelocityof22.6m/s,passesthroughaceramicmonolithsubstratewithsquareshapedchannels,andthenexitsthroughtheoutlet.

Whiletheflowintheinletandoutletsectionsisturbulent,theflowthroughthesubstrateislaminarandischaracterizedbyinertialandviscouslosscoefficientsintheflow（X）direction.Thesubstrateisimpermeableinotherdirections,whichismodeledusinglosscoefficientswhosevaluesarethreeordersofmagnitudehigherthanintheXdirection.

SetupandSolution

Step1:

Grid

1.Readthemeshfile（catalyticconverter.msh）.

File/Read/Case...

2.Checkthegrid.Grid/Check

FLUENTwillperformvariouschecksonthemeshandreporttheprogressintheconsole.Makesurethattheminimumvolumereportedisapositivenumber.

3.Scalethegrid.

Grid!

Scale...

（a）SelectmmfromtheGridWasCreatedIndrop-downlist.

（b）ClicktheChangeLengthUnitsbutton.Alldimensionswillnowbeshowninmillimeters.

（c）ClickScaleandclosetheScaleGridpanel.

4.Displaythemesh.Display/Grid...

（a）Makesurethatinlet,outlet,substrate-wall,andwallareselectedintheSurfacesselectionlist.

（b）ClickDisplay.

（c）RotatetheviewandzoomintogetthedisplayshowninFigure7.2.

（d）ClosetheGridDisplaypanel.

Thehexmeshonthegeometrycontainsatotalof34,580cells.

Step2:

Models

1.Retainthedefaultsolversettings.Define/Models/Solver...

2.Selectthestandardk-εturbulencemodel.Define/Models/Viscous...

Step3:

Materials

1.AddnitrogentothelistoffluidmaterialsbycopyingitfromtheFluentDatabaseformaterials.Define/Materials...

（a）ClicktheFluentDatabase...buttontoopentheFluentDatabaseMaterialspanel.

i.Selectnitrogen（n2）fromthelistofFluentFluidMaterials.

ii.ClickCopytocopytheinformationfornitrogentoyourlistoffluidmaterials.

iii.ClosetheFluentDatabaseMaterialspanel.

（b）ClosetheMaterialspanel.

Step4:

BoundaryConditions.Define/BoundaryConditions...

1.Settheboundaryconditionsforthefluid（fluid）.

（a）SelectnitrogenfromtheMaterialNamedrop-downlist.

（b）ClickOKtoclosetheFluidpanel.

2.Settheboundaryconditionsforthesubstrate（substrate）.

（a）SelectnitrogenfromtheMaterialNamedrop-downlist.

（b）EnablethePorousZoneoptiontoactivatetheporouszonemodel.

（c）EnabletheLaminarZoneoptiontosolvetheflowintheporouszonewithoutturbulence.

（d）ClickthePorousZonetab.

i.MakesurethattheprincipaldirectionvectorsaresetasshowninTable7.1.Usethescrollbartoaccessthefieldsthatarenotinitiallyvisibleinthepanel.

ii.EnterthevaluesinTable7.2fortheViscousResistanceandInertialResistance.Scrolldowntoaccessthefieldsthatarenotinitiallyvisibleinthepanel.

（e）ClickOKtoclosetheFluidpanel.

3.Setthevelocityandturbulenceboundaryconditionsattheinlet（inlet）.

（a）Enter22.6m/sfortheVelocityMagnitude.

（b）SelectIntensityandHydraulicDiameterfromtheSpecificationMethoddropdownlistintheTurbulencegroupbox.

（c）Retainthedefaultvalueof10%fortheTurbulentIntensity.

（d）Enter42mmfortheHydraulicDiameter.

（e）ClickOKtoclosetheVelocityInletpanel.

4.Settheboundaryconditionsattheoutlet（outlet）.

（a）Retainthedefaultsettingof0forGaugePressure.

（b）SelectIntensityandHydraulicDiameterfromtheSpecificationMethoddropdownlistintheTurbulencegroupbox.

（c）Enter5%fortheBackflowTurbulentIntensity.

（d）Enter42mmfortheBackflowHydraulicDiameter.

（e）ClickOKtoclosethePressureOutletpanel.

5.Retainthedefaultboundaryconditionsforthewalls（substrate-wallandwall）andclosetheBoundaryConditionspanel.

Step5:

Solution

1.Setthesolutionparameters.Solve/Controls/Solution...

（a）RetainthedefaultsettingsforUnder-RelaxationFactors.

（b）SelectSecondOrderUpwindfromtheMomentumdrop-downlistintheDiscretizationgroupbox.

（c）ClickOKtoclosetheSolutionControlspanel.

2.Enabletheplottingofresidualsduringthecalculation.Solve/Monitors/Residual...

（a）EnablePlotintheOptionsgroupbox.

（b）ClickOKtoclosetheResidualMonitorspanel.

3.Enabletheplottingofthemassflowrateattheoutlet.

Solve/Monitors/Surface...

（a）SettheSurfaceMonitorsto1.

（b）EnablethePlotandWriteoptionsformonitor-1,andclicktheDefine...buttontoopentheDefineSurfaceMonitorpanel.

i.SelectMassFlowRatefromtheReportTypedrop-downlist.

ii.SelectoutletfromtheSurfacesselectionlist.

iii.ClickOKtoclosetheDefineSurfaceMonitorspanel.

（c）ClickOKtoclosetheSurfaceMonitorspanel.

4.Initializethesolutionfromtheinlet.Solve/Initialize/Initialize...

（a）SelectinletfromtheComputeFromdrop-downlist.

（b）ClickInitandclosetheSolutionInitializationpanel.

5.Savethecasefile（catalyticconverter.cas）.File/Write/Case...

6.Runthecalculationbyrequesting100iterations.Solve/Iterate...

（a）Enter100fortheNumberofIterations.

（b）ClickIterate.

TheFLUENTcalculationwillconvergeinapproximately70iterations.Bythispointthemassflowratemonitorhasattendedout,asseeninFigure7.3.

（c）ClosetheIteratepanel.

7.Savethecaseanddatafiles（catalyticconverter.casandcatalyticconverter.dat）.

File/Write/Case&Data...

Note:

Ifyouchooseafilenamethatalreadyexistsinthecurrentfolder,FLUENT

willpromptyouforconfirmationtooverwritethefile.

Step6:

Post-processing

1.Createasurfacepassingthroughthecenterlineforpost-processingpurposes.

Surface/Iso-Surface...

（a）SelectGrid...andY-CoordinatefromtheSurfaceofConstantdrop-downlists.

（b）ClickComputetocalculatetheMinandMaxvalues.

（c）Retainthedefaultvalueof0fortheIso-Values.

（d）Entery=0fortheNewSurfaceName.

（e）ClickCreate.

2.Createcross-sectionalsurfacesatlocationsoneithersideofthesubstrate,aswellasatitscenter.

Surface/Iso-Surface...

（a）SelectGrid...andX-CoordinatefromtheSurfaceofConstantdrop-downlists.

（b）ClickComputetocalculatetheMinandMaxvalues.

（c）Enter95forIso-Values.

（d）Enterx=95fortheNewSurfaceName.

（e）ClickCreate.

（f）Inasimilarmanner,createsurfacesnamedx=130andx=165withIso-Valuesof130and165,respectively.ClosetheIso-Surfacepanelafterallthesurfaceshavebeencreated.

3.Createalinesurfaceforthecenterlineoftheporousmedia.

Surface/Line/Rake...

（a）EnterthecoordinatesofthelineunderEndPoints,usingthestartingcoordinateof（95,0,0）andanendingcoordinateof（165,0,0）,asshown.

（b）Enterporous-clfortheNewSurfaceName.

（c）ClickCreatetocreatethesurface.

（d）ClosetheLine/RakeSurfacepanel.

4.Displaythetwowallzones（substrate-wallandwall）.Display/Grid...

（a）DisabletheEdgesoption.

（b）EnabletheFacesoption.

（c）DeselectinletandoutletinthelistunderSurfaces,andmakesurethatonlysubstrate-wallandwallareselected.

（d）ClickDisplayandclosetheGridDisplaypanel.

（e）RotatetheviewandzoomsothatthedisplayissimilartoFigure7.