fluent噪声培训资料(上)

Tutorial:ModelingFlow-Induced(Aeroacoustic)Noise

ProblemsUsingFLUENT

Introduction

Thistutorialdemonstrateshowtomodel2Dturbulentflowacrossacircularcylinderusing

largeeddysimulation(LES)andcomputeflow-induced(aeroacoustic)noiseusingFLUENT’s

acousticsmodel.

Youwilllearnhowto:

•Performa2Dlargeeddysimulation.

•Setparametersforanaeroacousticcalculation.

•Saveacousticsourcedataforanacousticcalculation.

•Calculateacousticpressuresignals.

•Postprocessaeroacousticresults.

Prerequisites

ThistutorialassumesthatyouarefamiliarwiththeFLUENTinterfaceandthatyouhavea

goodunderstandingofbasicsetupandsolutionprocedures.Somestepswillnotbeshown

explicitly.

Inthistutorialyouwillusetheacousticsmodel.Ifyouhavenotusedthisfeaturebefore,

firstreadChapter21,PredictingAerodynamicallyGeneratedNoise,oftheFLUENT6.2

User’sGuide

c󰀁FluentInc.May11,20051ModelingFlow-Induced(Aeroacoustic)NoiseProblemsUsingFLUENT

ProblemDescription

Theproblemconsidersturbulentairflowovera2Dcircularcylinderatafreestreamve-

locity(U)of69.2m/s.Thecylinderdiameter(D)is1.9cm.TheReynoldsnumberbased

onthediameteris90,000.Thecomputationaldomain(Figure1)extends5Dupstreamand

20Ddownstreamofthecylinder.

U = 69.2 m/sD = 1.9 cm

Figure1:ComputationalDomain

Preparation

1.Copythefilecylinder2d.mshtoyourworkingdirectory.

2.Startthe2DversionofFLUENT.

Approximately2.5hoursofCPUtimeisrequiredtocompletethistutorial.Ifyouare

interestedexclusivelyinlearninghowtosetuptheacousticsmodel,youcanreducethe

computingtimerequirementsconsiderablybystartingatStep7andusingtheprovidedcase

anddatafiles.

2c󰀁FluentInc.May11,2005ModelingFlow-Induced(Aeroacoustic)NoiseProblemsUsingFLUENT

Step1:Grid

1.Readthegridfilecylinder2d.msh.File−→Read−→Case...

AsFLUENTreadsthegridfile,itwillreportitsprogressintheconsolewindow.

Sincethegridforthistutorialwascreatedinmeters,thereisnoneedtorescalethe

grid.Checkthatthedomainextendsinthex-directionfrom-0.095mto0.38m.

2.Checkthegrid.

Grid−→Check

FLUENTwillperformvariouschecksonthemeshandwillreporttheprogressinthe

consolewindow.Payparticularattentiontothereportedminimumvolume.Make

surethisisapositivenumber.

3.Reorderthegrid.

Grid−→Reorder−→Domain

Tospeedupthesolutionprocedure,themeshshouldbereordered,whichwillsubstan-

tiallyreducethebandwidthandmakethecoderunfaster.

FLUENTwillreportitsprogressintheconsolewindow:>>ReorderingdomainusingReverseCuthill-McKeemethod:zones,cells,faces,done.Bandwidthreduction=32634/253=128.99Done.

c󰀁FluentInc.May11,20053ModelingFlow-Induced(Aeroacoustic)NoiseProblemsUsingFLUENT

4.Displaythegrid.Display−→Grid...

(a)Displaythegridwiththedefaultsettings(Figure2).

Usethemiddlemousebuttontozoominontheimagesoyoucanseethemesh

nearthecylinder(Figure3).

Grid FLUENT 6.2 (2d, segregated, LES, unsteady)

Figure2:GridDisplay

4c󰀁FluentInc.May11,2005ModelingFlow-Induced(Aeroacoustic)NoiseProblemsUsingFLUENT

Grid FLUENT 6.2 (2d, segregated, LES, unsteady)

Figure3:TheGridAroundtheCylinder

QuadrilateralcellsareusedforthisLESsimulationbecausetheygenerateless

numericaldiffusionthantriangularcells.Thecellsizeshouldbesmallenoughto

capturetherelevantturbulencelengthscales,andtomakethenumericaldiffusion

smallerthanthesubgrid-scaleturbulenceviscosity.Themeshforthistutorial

hasbeenkeptcoarseinordertospeedupthecalculations.AhighqualityLES

simulationwillrequireafinermeshnearthecylinderwall.

c󰀁FluentInc.May11,20055ModelingFlow-Induced(Aeroacoustic)NoiseProblemsUsingFLUENT

Step2:Models

1.Selectthesegregatedsolverwithsecond-orderimplicitunsteadyformulation.Define−→Models−→Solver...

(a)RetainthedefaultselectionofSegregatedunderSolver.

(b)UnderTime,selectUnsteady.

(c)UnderTransientControls,selectNon-IterativeTimeAdvancement.

(d)UnderUnsteadyFormulation,select2nd-OrderImplicit.

(e)UnderGradientOption,selectNode-Based.

(f)ClickOK.

6c󰀁FluentInc.May11,2005ModelingFlow-Induced(Aeroacoustic)NoiseProblemsUsingFLUENT

2.SelecttheLESturbulencemodel.

TheLESturbulencemodelisnotavailablebydefaultfor2Dcalculations.Youcan

makeitavailableintheGUIbytypingthefollowingcommandintheFLUENTconsole

window:

(rpsetvar’les-2d?#t)Define−→Models−→Viscous...

(a)UnderModel,selectLargeEddySimulation.

(b)RetainthedefaultoptionofSmagorinsky-LillyunderSubgrid-ScaleModel.

(c)Retainthedefaultvalueof0.1forthemodelconstantCs.

(d)ClickOK.

YouwillseeaWarningdialogbox,statingthatBoundedCentral-Differencingis

defaultformomentumwithLES/DES.ClickOK.

TheLESturbulencemodelisrecommendedforaeroacousticsimulationsbecauseLES

resolvesalleddieswithscaleslargerthanthegridscale.Therefore,widebandaeroa-

cousticnoisecanbepredictedusingLESsimulations.

c󰀁FluentInc.May11,20057