Tutorial:BroadbandNoiseModeling
Purpose
Thepurposeofthistutorialistoprovideguidelinesandrecommendationsforthebasicsetupandsolutionprocedureforsolvinganacousticsfieldgeneratedfromasedancarusingthebroadbandnoisemodel.Theproblemisinitiallysolvedforsteadystate,andthenthebroadbandacousticmodelisincludedinthecalculationtoperformpostprocessing.
Prerequisites
Thistutorialassumesthatyouarefamiliarwiththeuserinterface,basicsetupandsolutionproceduresinFLUENT.Thistutorialdoesnotcovermechanicsofusingthebroadbandnoisemodel,butfocusesonsettinguptheproblemforasedancarandperformingpostprocessing.Italsoassumesthatyouhaveabasicunderstandingofaeroacousticphysics.
IfyouhavenotusedFLUENTbefore,itwouldbehelpfultofirstreviewFLUENT6.2User’sGuideandFLUENT6.2TutorialGuide.
ProblemDescription
TheprobleminvolvesasedancarmodelasshowninFigure1.Thecaristravelingat70milesperhour.Youwillstudyonlytheacousticsfieldgeneratedbythemotionofthecartohighlightthenoisesourceonthesedanbody,thereforethemirrorsandthewheelsofthecarareignored.
Figure1:TheSedanCar
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Preparation
1.Copythemeshfile,sedan-acoustics.mshfromtheinputfileintoyourworkingdi-rectory.2.Startthe3DversionofFLUENT.
SetupandSolution
Step1:Grid
1.Readthemeshfile,sedan-acoustics.msh.
File−→Read−→Case...2.Checkthegrid.
Grid−→Check...
3.Keepdefaultscaleforthegrid.
Grid−→Scale...4.Displaythegrid.
Display−→Grid...
YXZGridFLUENT 6.2 (3d, segregated, lam)Figure2:GridDisplay
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Step2:Models
1.Keepthedefaultsolversettings.
Define−→Models−→Solver...
2.Enablethestandardk-epsilonturbulencemodel.
Define−→Models−→Viscous...Step3:MaterialsDefine−→Materials...
1.KeepthedefaultselectionofairintheMaterialspanel.Step4:OperatingConditionsDefine−→OperatingConditions...
1.Keepthedefaultoperatingconditions.Step5:BoundaryConditionsDefine−→BoundaryConditions...
1.Settheboundaryconditionsforvelocityinlet(inlet).
(a)UnderZone,selectinlet.
TheTypewillbereportedasvelocity-inlet.(b)ClickSet...toopentheVelocityInletpanel.
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i.Specifyavalueof31forVelocityMagnitude.
ii.SelectIntensityandLengthScaleintheTurbulenceSpecificationMethoddrop-downlist.iii.Specifyavalueof2and0.35forTurbulenceIntensityandTurbulenceLength
Scalerespectively.
2.Settheboundaryconditionsforpressureoutlet(outlet)asshowninthepanel.
3.Keepthedefaultboundaryconditionsforotherwalls.
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Step6:Solution
1.Retainthedefaultunder-relaxationfactorsanddiscretizationschemes.
Solve−→Controls−→Solution...
2.Enabletheplottingofresidualsduringthecalculation(Figure3).
Solve−→Monitors−→Residual...3.Initializethesolution.
Solve−→Initialize−→Initialize...
(a)SelectinletintheComputeFromdrop-downlistandclickInit.4.Writethecasefile(sedan.cas.gz).
5.Startthecalculationbyrequesting70iterations.
Solve−→Iterate...
6.Writethedatafile(sedan.dat.gz).
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Residualscontinuityx-velocityy-velocityz-velocitykepsilon1e+031e+021e+011e+001e-011e-021e-031e-041e-051e-06YXZ010203040506070IterationsScaled ResidualsFLUENT 6.2 (3d, segregated, ske)Figure3:ScaledResiduals
Step7:EnabletheBroadbandAcousticModelDefine−→Models−→Acoustics...
1.UnderModel,selectBroadbandNoiseSources.
(a)Specifyavalue4e-10forReferenceAcousticPower(w).(b)SettheNumberofRealizationsto50.
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(c)RetainthedefaultvaluesfortherestofthemodelconstantsandclickOKto
closethepanel.Step8:Postprocessing
1.DisplaythefilledcontoursofAcousticsPowerLevel(dB)onthesurfacesofthesedancar,i.e.,front,rear,andcabinet(Figure4).
Display−→Contours...
(a)UnderOptions,selectFilled.
(b)SelectAcoustics...andAcousticPowerLevel(dB)fromtheContoursofdrop-down
lists.(c)UnderSurfaces,selectfront,rear,andcabinet.(d)ClickDisplay.
2.Similarly,displaythefilledcontoursofSurfaceAcousticsPowerLevel(dB)(Figure5),andLilley’sTotalNoiseSource(Figure6)onthesurfacesofthesedancar.
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5.06e+014.80e+014.55e+014.30e+014.05e+013.79e+013.54e+013.29e+013.03e+012.78e+012.53e+012.28e+012.02e+011.77e+011.52e+011.26e+011.01e+017.58e+005.06e+00Y2.53e+000.00e+00ZXContours of Acoustic Power Level (dB)FLUENT 6.2 (3d, segregated, ske)Figure4:ContoursofAcousticPowerLevel
5.30e+015.04e+014.77e+014.51e+014.24e+013.98e+013.71e+013.45e+013.18e+012.92e+012.65e+012.39e+012.12e+011.86e+011.59e+011.33e+011.06e+017.95e+005.30e+00Y2.65e+000.00e+00ZXContours of Surface Acoustic Power Level (dB)FLUENT 6.2 (3d, segregated, ske)Figure5:ContoursofSurfaceAcousticsPowerLevel
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6.21e+135.90e+135.59e+135.28e+134.97e+134.66e+134.35e+134.04e+133.73e+133.42e+133.11e+132.80e+132.48e+132.17e+131.86e+131.55e+131.24e+139.32e+126.21e+123.11e+121.03e+06YXZContours of Lilley’s Total Noise Source (1/s3)FLUENT 6.2 (3d, segregated, ske)Figure6:ContoursofLilley’sTotalNoiseSource
Summary
ThistutorialdemonstratedtheuseofFLUENT’sbroadbandnoiseacousticmodeltosolveanacousticsfieldgeneratedfromasedancar.Youhavelearnedhowtosetuptherelevantparametersandpostprocessthenoisesignalstohighlightthesourceofnoiseonthesedancarbody.
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