计算流体力学CFD外文翻译

******大学****届本科生毕业设计（论文）外文翻译1ComputationalFluidDynamics–orHowtoMakeaGoodBoatFastDavidVacantiThetermCFDisshowingupmoreoftenthesedaysinarticlesdescribingthedesigneffortsusedtomakeVolvo60roundtheworldracersandAmerica’sCupyachtsfaster.ComputationalFluidDynamicsorCFDactuallycoversagreatmanyengineeringspecialtiesandisnotthesoledomainofboatandshipdesign.InthisarticlewewillreviewwhattypesofCFDproductsexistandhopefullyprovidesomeunderstandingofwhenandhowCFDproductsarebestsuitedtoaproject.ComputationalFluidDynamicsistheapplicationofcomputerstothemodelingoffluidcharacteristicswheneitherthefluidisinmotionorwhenanobjectdisturbsafluid.Afewexamplesofafluidinmotionarewaterorchemicalflowinpipes,heatingandventilationsystemsconductingcooling,heatingorfreshairsuppliestoabuilding.Fluidsinmotionalsoincludeflameandfireeffectsincombustionorjetengines.Surprisedbythesefieldsofinterest?Whataboutexamplesofanobjectdisturbingafluid?Examplesincludestirringpaddlessubmergedinatankofwaterandeffluentinawastetreatmentplant,aircraftofallkinds,carsandtrucksathighwayorracingspeedsandevenmonohullsailboats,ship,multihullsailboatstonamebutafew.Obviously,anopenmindisimportantwhenconsideringwhatconstitutesafluid.Fluidscanexistingaseousandliquidstatesandsciencehasrecentlyfoundthatevensomesolidscanexhibitfluidlikecharacteristicsunderrightconditions.Scientistshavefoundthatsomeofthemostspectacularanddeadlylandslidesorrockfallsbehaveasafluidwhilethemassofstoneandsoilorsandisinmotion,onlytoreturntoamostdecidedlysolidformwhenthemotionsubsides.Thegeneralfieldoffluiddynamicsdiffersfromthefieldofboatdesigninonecriticalway.Onlyboatdesigndealswithavehiclepassingthroughthetwofluidsofairandwatersimultaneously.Ouratmosphereisacompressiblefluid,thoughnotatyachtingorevenhigh-poweredboatracingspeeds.Aircanchangeindensityaccordingtoaltitude,temperatureandhumidity.Waterisanincompressiblefluidthatcanvaryinviscosityaccordingtoitssalinityandtemperature.Formostofus,smalleffectssuchasvariablesalinityandtemperaturearenotofconcern,butcanmakethedifferencebetweenwinningandloosingamajorinternationalyachtrace.HowdoCFDprogramsWork?CFDprogramsarebasedonthelawsofphysics,suchasthelawofconservationofmomentum,andspecial“boundaryconditions”.Thelawofconservationofmomentumstates******大学****届本科生毕业设计（论文）外文翻译2thatthetotalmomentumofasystemremainsconstantregardlessofhowthesystemmaychange.Aboundaryconditionlimitshowandwhereafluidcantravel.Asimpleexampleisthatmotionofthefluidmustemaintangentorparalleltothesurfaceofanobjectpassingthroughit.Anotherexampleisthatpressureappliedbythefluidagainsttheobjectmustbeperpendiculartothesurfaceatallpoints.TheselawsandconditionsarecriticaltothedevelopmentofaCFDprogrambecausetheyallowanaerodynamicisttowriteequationsthatdescribethesystemthatisbeingstudied.Withoutthephysicallawsandboundaryconditionstherewouldbenowaytowriteequationsthatdescribefluidmotion.Thecomplexequationsthatresulttakeintoaccounttheviscosity,massandothercharacteristicsofthefluid.Theequationsarewrittenusingintegralanddifferentialcalculusandrequirespecializedcomputertechniquestosolvethem.Typicallytheprogrammerwritesanalgorithmthatmakesaseriesofestimatesusingalgorithmsthatiterativelysolvethesetsofequationsbylookingfor“balance”inthesystemofequations.Afinalanswerisobtainedwhenthealgorithmconvergesonasolutionwithanerrorthatissufficientlysmallforthedesiredaccuracy.Onceanalgorithmhasbeendevelopedtoimplementthelawsofmomentumandboundaryconditions,itcannotbeappliedtotheentiresurfaceofthehullandappendagesatonce.Thesurfaceareaofthehull,keelandrudderarebrokenintothousandsofsmallpatches(collectivelycalledamesh)andthealgorithmappliedtoeachpatch.Eachpatchinturninfluencesthefluidflowonthepatchareaofitsneighborsandthereforethesolutionmustaccountfortheconditionssurroundingthepatchcurrentlybeingsolved.Asaresulttheprogrammustsolveandresolvetheequationsforallofthepatchesuntilthesolutionobeysthephysicallawsandboundaryconditions.Sometimesthecomplexitiesofthelawsofphysicsaretoodifficulttoimplementallatthesametime.Asaresulttheaerodynamicistschoosetowriteprogramsthatmakecertainlimitingassumptionsthatpermittheprogrammingtobecomemorepracticalandstillresultinreasonableresults.Aspecificexamplearisesinthecaseofwhatactuallyhappenstofluidsverynearthesurfaceofanobject.Theboundarylayerasitiscalledexperiencesshearforcesintheobjectsdirectionoftravelthatresultinviscousdrag.TheseshearforcesaredescribedinaspecialsetofequationscalledtheNavierStokesrelationships.TheNavierStokesequationsaresufficientlycomplexthemselvesthatattemptingtoincludethemwithineveryaerodynamicsorhydrodynamicsprogramwouldmakethesolutionsnearlyimpossible.AsaresultthereareNavierStokesbasedprogramsthatspecificallyaddressviscousdragandPanelmethodprogramsthatcomputelift,wavedragandinduceddrag.Acompleteestimateofthedragencounteredbyaboatrequiresthedatasuppliedbybothprograms.******大学****届本科生毕业设计（论文）外文翻译3WhatdoCFDprogramsCalculate?Themostobviouscalculationthatwouldbeofinterestinboatdesignisthedeterminationofdragforces.Butdragcomesinseveralformsthatcaninclude,wave,viscous,andi