ABSTRACT
异丙基丙烯酰胺
Avarietyofdifferentpointsofviewaboutthemechanismofturbulencedragreductioninducedbythepolymerwereproposed,therepresentativetheoriesofwhichareviscositymechanismandelasticmechanismetc.Inthepresenttheviscositydragreductionandelasticdragreductionarestilloneofthethemesunderdebate.In
recentstudiesofpolymerdragreductioninwallturbulence,theeffectiveviscositytheorywasproposedbyL’VOVetaI(PRL,2004).Inthispaper,throughtheoreticalderivationalineareffectiveviscositymodelwasestablishedbasedonthistheoryanddescribepolymerdragreductionflowviathecouplingoft
hismodelandNavier—Stokesequation,researchofpolymerdragreductionisdonefromthepointofviewofviscosityeffects.
Usingeffectiveviscositymodel,numericalcalculationwasdonewithReynoldsStress
equationModeland
LargeEddySimulation,respectively.Inwhichtheeffectoftheboundary
layeronpolymerdragreductionWasstudiedbytheribstripsettingtodamagetheboundarylayer.First,thefurthervalidationofeffectiveviscositymodelwasundertakenbycomparingwithdirectnumericalsimulationresultsusingtheFENE·Pmodelunderthesameflowcondition.Byanalysisofthe
如来
神掌之宇宙争雄
calculationresults,themainconclusionsaregivenasfollowing:(1)Thelineareffectiveviscositychangesthedistributionofmeanvelocityinthechannel,givesathickerelasticbufferlayerandreducestheReynoldsshear
stress.ThemeanvelocityprofileareclosetoVirk’Smaximumdragreductionasymptote,andtendsto
离婚冷静期
细则laminarflowvelocityprofilewhenreachhilghdragreduction(ormaximumdragreduction).(2)Throughtheanalysisofstressesitisfoundthatthelineareffectiveviscositychangestressbalancingintheturbulenceflows,whichreducetheReynoldsstressaccountsfortheproportionofthetotal
shearstress,increasetheviscousshearstress.Althoughviscousdissipationincreases,butincreasetheflowstabilityatthesametime.
(3)Throughtheanalysisofturbulenceintensityitisfoundthatthelineareffectiveviscositycanreflectthe
characteristicsoflowdragreductionflow,andelasticeffectsshouldbeconsideredinhighdragreduction,buttheviscouseffectsshouldplaytheleadingroleinthedragreduction.TheY-direction(verticalwalldirection)turbulenceintensitydirectlyinfluencethedragreduction,anditiscloselyrelatedtoY-directionelongationofpolymer,勘,whichsuggests勘directlyaffectthedragreduction,andwhichisconsistentwiththetheoreticalbasisoftheeffectiveviscosity.
(4)Thelineareffectiveviscositycanreduceturbulentburstsfrequency,andturbulent
Ill
血尿素
羟氨苄
青霉素胶囊