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ThePotentialofLargeEddySimulationforthe
ModelingofWallBoundedFlows
EugenedeVilliers
ThermofluidsSection
DepartmentofMechanicalEngineering
ImperialCollegeofScience,TechnologyandMedicine
25thJuly2006
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Abstract
LargeEddySimulation (LES)hasshowngreatpromiseinthecalculationoftraditionally
di±cultturbulentcases,suchasunsteadyandrecirculatingflowsandforaeroacoustic
applications.Unfortunately,thisaddedaccuracy,(thoughmuchlessexpensivethan Di-
rectNumericalSimulations (DNS))comesataconsiderablecomputationalcostincrease
whencomparedtotheconventional ReynoldsAverage (RANS)approach.Althoughitis
bynomeanstheonlyfactorleadingtothisincreasedcost,thewayinwhichLESinter-
actswithwallboundarieshasbeenidentifiedasthemajorcontributortothisproblem.
Inanattempttoaddressthisissue,manyturbulenceresearchershaveinvestigatedthe
requirementsande®ectsofsimplifyingtheaforementionedinteraction,whichhastodate
metwithvaryingdegreesofsuccess.
Thecurrentworkaimstocontributetothise®ort,withthemaingoalofascertaining
whetherLEScane®ectivelybeusedintheneartermtomodelaerodynamicflowsofthe
typeassociatedwithautomobiles.Inadditiontoprovidingmoreaccurateaerodynamic
results,suchamethodologyshouldalsoallowthecalculationofaero-acousticnoiseforthe
problemunderinvestigation.Largegridsizesnecessitatedbywellresolvedaerodynamic
simulationsofsuchhighReynoldsnumberflowsmakethemgenerallyunfeasiblegiven
currentCPUspeeds.Thisprojectattemptstoaddressthisissueintwoways:firstly,
throughtheapplicationofapproximatewalltreatmentsandsecondlythroughimproved
meshdistribution.
Severalsuchwalltreatmentsareinvestigatedandthemostpromisingareimplemented
forfurthertesting.Inaddition,embeddedmeshrefinementisemployedtoresolveflow
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regionsofinterest,whilestillmaintainingareasonableoverallgridsize.Verygoodagree-
mentbetweenexperimentaldataandcomputationalresultsisobservesforalltestcases
althoughrequirementsintermsofwalltreatmentsandturbulencemodellingdi®er.Sig-
nificantly,largeeddysimulationisshowntobeane±cienttoolforthepredictionof
aero-acousticnoisesourcesandotherunsteadyflowphenomena.
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Acknowledgements
Iwishtoexpressmygratitudetomysupervisor,Prof.DavidGosman,fortheincredible
amounthehastaughtmeduringthecourseofthisthesis.Ithasbeenanexceedingly
rewardingexperience.
IwouldliketothankHenryWeller,notonlyfordevelopingandmakingFOAMavail-
able,butalsoforhisfeedbackandmanyfruitfulldiscussionsonallmattersCFDrelated.
ThanksalsotoDr.HrvJasak,co-developerofFOAM,whokindlyo®eredtoproofread
mythesis.ToeveryoneelsewithwhomIsharedRoom600:yourcollaborationand
companionshiphasbeeninvaluableincompletingthiswork.
TomywifeLieslIameternallygratefulforthemanyyearsofpatienceandunfailing
support.Dr.MichaelWessels,yourencouragementandfriendshipisthankfullyacknowl-
edged.Finally,totheprojectsponsorDaimlerChrysler:thankyouformakingitall
possible.
EugenedeVilliers
July2006
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