fluent中多孔介质设置问题和算例.docx
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fluent中多孔介质设置问题和算例.docx
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fluent中多孔介质设置问题和算例
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:
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,createsurfacesnam
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