Flat Plate Boundary Layer.docx
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Flat Plate Boundary Layer.docx
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FlatPlateBoundaryLayer
FlatPlateBoundaryLayer
ProblemSpecification
Consideraflowoveraninfinitelythinflatplatewithalengthof1meter.Thefluidisflowinginthex-directionwithavelocityof1m/s.TheReynold'snumberforthisproblemis1e-4.
Step1:
CreateGeometryinGAMBIT
UnderConstruction
Step2:
MeshGeometryinGAMBIT
Underconstruction
Step3:
SpecifyBoundaryTypesinGAMBIT
Underconstruction
Step4:
SetUpProbleminFLUENT
Ifyouhaveskippedthepreviosmeshgenerationsteps1-3,youcandownloadthemeshbyright-clickingonthislink.SavethefileasplateBL.msh.
LaunchFLUENT
LabApps>FLUENT6.3.26
Select2ddp(2D,double-precisionversion)fromthelistofoptionsandclickRun.
ImportFile
MainMenu>File>Read>Case...
NavigatetoyourworkingdirectoryandselecttheplateBL.mshfile.ClickOK.
Checkthatthedisplayedinformationisconsistentwithourexpectations.
AnalyzeGrid
First,wecheckthegridtomakesurethattherearenoerrors.
MainMenu>Grid>Check
Anyerrorsinthegridwouldbereportedatthistime.Checktheoutputandmakesurethattherearenoerrorsreported.
Grid>Info>Size
Howmanycellsandnodesdoesthegridhave?
Display>Grid
DefineProperties
Define>Models>Solver...
Usethedefaultsetting.ClickOK.
Define>Models>Viscous
SelectLaminarunderModel.
ClickOK.
Define>Models>Energy
UsethedefaultandclickOK.
Define>Materials
MakesureairisselectedunderFluidMaterials.SetDensityto1.00andViscosityto1e-4sothatwecangetReof1e4.
ClickChange/Create.
Define>OperatingConditions
Usethedefaultvalue.ClickOK.
Define>BoundaryConditions
Setinlettovelocity-inletboundarytype.ThenclickSet...Setthevelocitymagnitudeto1m/s.Setoutlettopressure-outletboundary.Usegagepressureof0Pa.Usethedefaultvalueofwallfortheplate.Setthetoptosymmetryboundarytype.Symmetryboundaryconditionmeansthatthecomponentnormaltothewalliszero.
Step5:
Solve!
Solve>Control>Solution
We'lluseasecond-orderdiscretizationscheme.UnderDiscretization,setMomentumtoSecondOrderUpwind.
ClickOK.
Solve>Initialize>Initialize...
Usetheinletconditionsasourintialguessvalue.SelectinletunderComputeFrom.
ClickInit.
We'lliteratethesolutionuntiltheresidualforeachequationfallsbelow1e-6.
Solve>Monitors>Residual...
SetAbsoluteCriteriaforallequationsto1e-6.
Also,underOptions,selectPlot.Thiswillplottheresidualsinthegraphicswindowastheyarecalculated,givingyouavisualfeelforif/howtheiterationsareproceedingtoconvergence.
ClickOK.
MainMenu>File>Write>Case...
ThiswillsaveyourFLUENTsettingsandthemeshtoa"case"file.TypeinplateBL.casforCaseFile.ClickOK.
Solve>Iterate
SettheNumberofIterationsto1000.ClickIterate.
Theresidualsforeachiterationareprintedoutaswellasplottedinthegraphicswindowastheyarecalculated.
Savethesolutiontoadatafileaftersolutionisconverged:
MainMenu>File>Write>Data...
EnterplateBL.datforDataFileandclickOK.Checkthatthefilehasbeencreatedinyourworkingdirectory.Youcanretrievethecurrentsolutionfromthisdatafileatanytime.
Step6:
AnalyzeResults
PlotVelocityVectors
Let'splotthevelocityvectorsobtainedfromtheFLUENTsolution.
Display>Vectors
Zoominalittleusingthemiddlemousebuttontopeermorecloselyatthevelocityvectors.
Remembertosavetheimageusing
MainMenu>File>Hardcopy
Nowwewilldisplaythepressurecoefficientcontour.Firstsetthereferencevelocity.
Report>ReferenceValues
SelectinletunderComputeFrom
Display>Contours...
SelectPressure...andStaticPressurefromunderContoursOf.ThenselectPressureCoeffient.CheckFilledboxandsetLevelsto90.
Zoominattheleadingedge.
Whyisthepressurenotconstantattheleadingedgeoftheplate?
Nowwewillplottheskinfrictioncoefficientalongtheflatplate.
Plot>XYPlot
ChangePressuretoWallFluxes.AfterthatchangeWallShearStresstoSkinFrictionCoefficient.UnderSurfaces,selectplate.ClickPlot.
(Clickpictureforlargerimage)
ComparewithskinfrictionwiththeBlasiussolution.Loadthefileandplot.
Also,youcanchangethesymbolintolinesbygoingtoCurves...andclickonthecurrespondingpatternthatyoulike.IncreasetheWeightto3forreadability.Bothresultsshouldbefairlysimilar.
(Clickpictureforlargerimage)
Nowwewilllookatthevelocityalongtheplateatoutlet.
Plot>XYPlot
UncheckedPositiononXAxisandcheckPositiononYAxis.UnderPlotDirection,setXto0andYto1.UnderXAxisFunction,selectVelocity...AfterthatchangeVelocityMagnitudetoXVelocity.Finallyundersurface,clickoutlet.Beforewearereadytoplot,clickontheAxes...andrescaleyaxisfrom0to0.12.Also,checkedtheMajorRulesandMinorRulesforxandy.
ClickApplyandPlot.
(Clickpictureforlargerimage)
TocomparewiththeBlasiussolution,clickLoadFile...andselectthecorrectfile(title"SkinFrictionCoefficient")
(labels"Position""SkinFrictionCoefficient")
((xy/key/label"Blasius")
0.02000.04695189
0.04000.03320000
0.06000.02710769
0.08000.02347595
0.10000.02099752
0.12000.01916803
0.14000.01774615
0.16000.01660000
0.18000.01565063
0.20000.01484749
0.22000.01415653
0.24000.01355384
0.26000.01302211
0.28000.01254842
0.30000.01212293
0.32000.01173797
0.34000.01138751
0.36000.01106667
0.38000.01077150
0.40000.01049876
0.42000.01024574
0.44000.01001018
0.46000.00979015
0.48000.00958401
0.50000.00939038
0.52000.00920802
0.54000.00903590
0.56000.00887307
0.58000.00871875
0.60000.00857220
0.62000.00843281
0.64000.00830000
0.66000.00817328
0.68000.00805218
0.70000.00793632
0.72000.00782532
0.74000.00771884
0.76000.00761660
0.78000.00751832
0.80000.00742375
0.82000.00733265
0.84000.00724483
0.86000.00716010
0.88000.00707826
0.90000.00699917
0.92000.00692268
0.94000.00684864
0.96000.00677692
0.98000.00670741
1.00000.00664000
(Clickpictureforlargerimage)
Whatisthenoticeablydifferentbetweentwosolutions?
Whyisthevelocityovershoot1forFLUENT'ssolution?
Nowwewillcomparethevelocityprofileattwosections.Createanothersectioninthemiddleoftheplate.
Surface>Line/Rake
Checkthelinetoolsboxandsettheinitialcoordinateof(0.5,0)tofinalcoordinateof(0.5,0.5).UnderNewSurfaceName,typeinx_0.5.
Wecannowplotcancomparethevelocityprofileatthemidpointandtheoutletoftheflow.
Plot>XYPlot
UnderSurfaces,selectoutletandx_0.5andPlot.
(Clickpictureforlargerimage)
Step7:
VerifyResults
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