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Tutorial:ModelingFlow-Induced(Aeroacoustic)NoiseProblemsUsingFLUENTIntroductionThistutorialdemonstrateshowtomodel2Dturbulentflowacrossacircularcylinderusinglargeeddysimulation(LES)andcomputeflow-induced(aeroacoustic)noiseusingFLUENT’sacousticsmodel.Youwilllearnhowto:•Performa2Dlargeeddysimulation.•Setparametersforanaeroacousticcalculation.•Saveacousticsourcedataforanacousticcalculation.•Calculateacousticpressuresignals.•Postprocessaeroacousticresults.PrerequisitesThistutorialassumesthatyouarefamiliarwiththeFLUENTinterfaceandthatyouhaveagoodunderstandingofbasicsetupandsolutionprocedures.Somestepswillnotbeshownexplicitly.Inthistutorialyouwillusetheacousticsmodel.Ifyouhavenotusedthisfeaturebefore,firstreadChapter21,PredictingAerodynamicallyGeneratedNoise,oftheFLUENT6.2User’sGuidecFluentInc.May11,20051ModelingFlow-Induced(Aeroacoustic)NoiseProblemsUsingFLUENTProblemDescriptionTheproblemconsidersturbulentairflowovera2Dcircularcylinderatafreestreamve-locity(U)of69.2m/s.Thecylinderdiameter(D)is1.9cm.TheReynoldsnumberbasedonthediameteris90,000.Thecomputationaldomain(Figure1)extends5Dupstreamand20Ddownstreamofthecylinder.U=69.2m/sD=1.9cmFigure1:ComputationalDomainPreparation1.Copythefilecylinder2d.mshtoyourworkingdirectory.2.Startthe2DversionofFLUENT.Approximately2.5hoursofCPUtimeisrequiredtocompletethistutorial.Ifyouareinterestedexclusivelyinlearninghowtosetuptheacousticsmodel,youcanreducethecomputingtimerequirementsconsiderablybystartingatStep7andusingtheprovidedcaseanddatafiles.2cFluentInc.May11,2005ModelingFlow-Induced(Aeroacoustic)NoiseProblemsUsingFLUENTStep1:Grid1.Readthegridfilecylinder2d.msh.File−→Read−→Case...AsFLUENTreadsthegridfile,itwillreportitsprogressintheconsolewindow.Sincethegridforthistutorialwascreatedinmeters,thereisnoneedtorescalethegrid.Checkthatthedomainextendsinthex-directionfrom-0.095mto0.38m.2.Checkthegrid.Grid−→CheckFLUENTwillperformvariouschecksonthemeshandwillreporttheprogressintheconsolewindow.Payparticularattentiontothereportedminimumvolume.Makesurethisisapositivenumber.3.Reorderthegrid.Grid−→Reorder−→DomainTospeedupthesolutionprocedure,themeshshouldbereordered,whichwillsubstan-tiallyreducethebandwidthandmakethecoderunfaster.FLUENTwillreportitsprogressintheconsolewindow:ReorderingdomainusingReverseCuthill-McKeemethod:zones,cells,faces,done.Bandwidthreduction=32634/253=128.99Done.cFluentInc.May11,20053ModelingFlow-Induced(Aeroacoustic)NoiseProblemsUsingFLUENT4.Displaythegrid.Display−→Grid...(a)Displaythegridwiththedefaultsettings(Figure2).Usethemiddlemousebuttontozoominontheimagesoyoucanseethemeshnearthecylinder(Figure3).GridFLUENT6.2(2d,segregated,LES,unsteady)Figure2:GridDisplay4cFluentInc.May11,2005ModelingFlow-Induced(Aeroacoustic)NoiseProblemsUsingFLUENTGridFLUENT6.2(2d,segregated,LES,unsteady)Figure3:TheGridAroundtheCylinderQuadrilateralcellsareusedforthisLESsimulationbecausetheygeneratelessnumericaldiffusionthantriangularcells.Thecellsizeshouldbesmallenoughtocapturetherelevantturbulencelengthscales,andtomakethenumericaldiffusionsmallerthanthesubgrid-scaleturbulenceviscosity.Themeshforthistutorialhasbeenkeptcoarseinordertospeedupthecalculations.AhighqualityLESsimulationwillrequireafinermeshnearthecylinderwall.cFluentInc.May11,20055ModelingFlow-Induced(Aeroacoustic)NoiseProblemsUsingFLUENTStep2:Models1.Selectthesegregatedsolverwithsecond-orderimplicitunsteadyformulation.Define−→Models−→Solver...(a)RetainthedefaultselectionofSegregatedunderSolver.(b)UnderTime,selectUnsteady.(c)UnderTransientControls,selectNon-IterativeTimeAdvancement.(d)UnderUnsteadyFormulation,select2nd-OrderImplicit.(e)UnderGradientOption,selectNode-Based.(f)ClickOK.6cFluentInc.May11,2005ModelingFlow-Induced(Aeroacoustic)NoiseProblemsUsingFLUENT2.SelecttheLESturbulencemodel.TheLESturbulencemodelisnotavailablebydefaultfor2Dcalculations.YoucanmakeitavailableintheGUIbytypingthefollowingcommandintheFLUENTconsolewindow:(rpsetvar’les-2d?#t)Define−→Models−→Viscous...(a)UnderModel,selectLargeEddySimulation.(b)RetainthedefaultoptionofSmagorinsky-LillyunderSubgrid-ScaleModel.(c)Retainthedefaultvalueof0.1forthemodelconstantCs.(d)ClickOK.YouwillseeaWarningdialogbox,statingthatBoundedCentral-DifferencingisdefaultformomentumwithLES/DES.ClickOK.TheLESturbulencemodelisrecommendedforaeroacousticsimulationsbecauseLESresolvesalleddieswithscaleslargerthanthegridscale.Therefore,widebandaeroa-cousticnoisecanbepredictedusingLESsimulations.cFluentInc.May11,20057ModelingFlow-Induced(Aeroacoustic)NoiseProblemsUsingFLUENTStep3:MaterialsYouwillusethedefaultmaterial,air,whichistheworkingfluidinthisproblem.Thedefaultpropertieswillbeusedforthissimulation.Define−→Materials...1.Retainthedefaultvalueof1.225forDensity.2.Retainthedefaultvalueof1.7894e-05forViscosity.Youcanmodifythefluidpropertiesforairorcopyanothermaterialfromthedatabaseifneeded.Fordetails,referthechapterPhysicalPopertiesintheFLUENTUser’sGuide.Step4:OperatingConditionsDefine−→OperatingConditions...1.Retainthedefaultvalueof101325PafortheOperatingPressure.Step5:BoundaryConditions1.Retainthedefaultco