简介：Anumericalsimulationisperformedtofindoutakeyvorticalstructureinthelaminar-turbulenttransition.Alow-speedstreakisgeneratedinsidealaminarboundarylayerusinganisolatedcuboidroughness,aimedatprovidinganenvironmentunstabletoouterdisturbances.Then,ashortdurationjetisissuedintotheboundarylayer.Whenthejetvelocityislow,somevorticesappearintheboundarylayer,butthetransitionoftheboundarylayerdoesnottakeplace.However,whenthejetvelocityexceedsacertainthreshold,twovorticesnewlyappearabovetheelongatedlegsofaV-shapedvortexandonlyoneofthemisstretchedandsurvives.Afterthat,vorticesaregeneratedoneafteranotheraroundthesurvivedone.Bycomparingthedecayedandthesurvivedvortices,itisfoundthatthedifferenceintheirheightsisthekeycharacteristicwhichleadstothetransition.

简介：Temporalmodedirectnumericalsimulationwasdonefortheprocessoflaminar-turbulenttransitioninanincompressibleboundarylayeronaflatplate.Theanalysisoftheresultsshowedthatduringthebreakdownprocessoflaminar-turbulenttransition,themodificationofthemeanflowprofilebythedisturbancesledtoaremarkablechangeinitsstabilitycharacteristics,manifestedinthesignificantenlargementofthelinearunstablezoneandthemaximumamplificationrate,andledtothatmanymoredisturbanceswereexcitedandenhancedrapidly,correspondinglytheturbulentenergyalsoincreasedrapidly,andthemeanflowprofilesevolvedswiftlyfromlaminartoturbulent.Itwasalsofoundthatiftheobliquewavesintheinitialdisturbancesdidnotformsymmetricalpairs,thesubsequentspan-wisemeanvelocitieswould,ingeneral,benonzeroduetononlinearinteraction,whichwouldhaveagreateffectonthestabilitycharacteristicsandalsoimpliedthattheturbulenceobtainedbydirectnumericalsimulationmightnotbefullyarandomprocess.

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简介：边界层转移一个完全倾斜的盘子借助于热转移大小被学习了。一个热流动传感器被开发了，为表面或流动的各种各样的类型转以便测量对流的热的效率。它在经常的温度的操作允许热流动的直接、快的大小。现在的纸报导传感器的发展并且在取决于外部流动的入射角的边界层介绍它的应用程序给转变的学习。在批评雷纳兹数字和压力坡度参数之间的一种指数的关系被发现了。

简介：Flowdistributionheadersplayamajorroleinheatexchangers.Theselectionofheaderdiameter,branchpipediameter,branchpipespacingetc.isbasedonthedesigner'sexperienceandgeneralguidelines.Theproperselectionoftheheaderdimensionswillyielduniformflowdistributioninheatexchangers,whichinturnwillenhancetheheatexchangerefficiency.Inthiswork,theflowdistributioninbranchpipesandthepressurevariationacrossthebranchpipesinlaminarandlowturbulenceregionisstudiedwithtwomodelsoftheinletdividingheaders.Whenthenumericalanalysishasbeenapplied,itsinabilitytopredictthenoflowconditionthroughthebranchpipesisrevealed.Theresultsarepresentedintheformofflowrateratiothroughbranchpipesandnondimensionalcoefficientsacrossbranchpipeswhichareusefultoapplytheexistingmathematicalmodelsforthepresentexperimentalsetup.

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简介：Theyear2016markedthe25thanniversaryoftheendoftheColdWarandthe15thanniversaryofthe9/11attack.Thoughinternationalrelationsareconstantlyadjusted,theworldisbynomeansmorestableandorderly.Internationalorderreshapingtriggeredbythe2008financialcrisisisdeepening,withchaosofvariouskindspoppinguphereandthere.Inthesociopoliticalfield,the'Trumpphenomenon'andBrexitindicateseriousweakeningoftheauthorityoftraditionalpoliticalsystemsandelites.Inmajorcountryrelationsandinternationalsecurity,theworldiswitnessingtheriseofemergingcountriesandtheandfalloftheWest,fiercerUS-RussiaandSino-USwrestlingofstrategicsignificance,andgreaterglobalandregionalsecurityrisks.Inglobalgovernance,whileadjustmentofUN-centeredglobalgovernanceislaboringalong,nationalrivalriestouchcoreissues,makingglobalgovernancemoreurgent.

简介：Theeffectsofheatlossonthestructureoflaminarflamelets,whicharetheconstitutiveelementsofturbulentflamesunderthemostcommonoperatingconditions,areinvestigatedfortypicalaeronauticalgas-turbineoperatingconditionsattake-off.Themagnitudeofheatlossisquantifiedviathe"enthalpydefect"measuredwithrespecttoanadiabaticflame.Aproceduretogeneratelaminarflameletswithanassignedenthalpydefectattheboundariesisdevisedandappliedtononpremixedpropane/airflames,aspropanereproducestheessentialfeaturesofhigherhydrocarboncombustion.Itisfound,contrarytocommonlyheldbeliefs,thattheenthalpydefecthasasignificanteffectontheconcentrationnotonlyofminorspecies,butalsoofmainreactionproducts.Sucheffectsarefoundingeneraltobemorepronouncedforfuel-richconditions.Animpactisanticipatedontheformationrateofnitricoxides.Theeffectsofscalardissipationratearealsodiscussed.

简介：Theoreticalandexperimentalinvestigationsofheattransferinflatcurvilinearchannelhavebeencarriedout.Linearandnon-lineareffectsofDeanvortexesonintensityofheattransferweretakenintoaccount.Thelineareffect,whichdescribeharmonic(sinuous)variationoftheheattransfercoefficientneartheconcavesurfaceofthechannelandthenon-lineareffectcausesthegeneralincreaseoftheheattransfercoefficientduetoaugmentationofheattransferengenderedbytheDeanvortexes.Forbotheffects,mathematicalrelationswereobtainedintheformofquadratures.Thesenumericalresultsweremodifiedtotheformconvenientinengineeringcalculations.TheinvestigationshaveshownthatbothlinearandnonlinearcomponentsgrowupwiththeDeannumber.NonlinearcomponentQ0Tincreasesmoreabruptly,whilethelinearoneQ1Tismoreconservative.Thisisaconfirmationofstabilityofvortexstructures.

简介：Antheoreticalinvestigationwasconductedtodetectthegas-solidinterfaceeffectonlaminarflowcharacteristicsforgasflowingthroughmicropassages.Inthewall-adjacentregion,thechangeinviscosityoffluidvsthedistancefromthewallsurface,asderivedfromthedkinetictheoryofgasesresultinsignificantinfluenceontheflowcharacteristicsinmicropassages.Amodelwasproposedtoaccountforthewalleffect.Analyticalexpressionsforvelocityprofilesandpressuredropwerederived,respectively,forlaminarflowofgasesinmicrotubesandinextremelynarrowparallelplaes.TheKnudsennumber,Kn,asacriterion,thattheflowcanbetreatedreasonablyasflowinmacrochannels,isdiscussed.

简介：Ageneralexpressionofthescintillationindexisproposedforopticalwavepropagatinginturbulentat-mosphereunderarbitraryfluctuationconditions.Theexpressiondependsonextremebehaviorsofthescintillationindicesunderbothweakandstrongfluctuations.ThemaximumscintillationindexintheonsetregionandthecorrespondingRytovindexcanbeevaluatedfromthegeneralexpression.Planeandsphericalwavesinthecasesofzeroandnon-zeroturbulenceinnerscalearegivenasexamplesforillustra-tionofthegeneralbehaviorsofscintillationindices.

简介：-Turbulentflowisabasicformoffluidmotionwidelyobservedinnature.Inhydraulicengineering,especiallyinthestudyofsedimentmovement,turbulenceisakeyproblem.Inthispaper,basedonthestochastictheoryofwallturbulencedevelopedbytheauthorandtheresultsbyotherinvestigators,fluc-tuationandmeanstructuresanddragcoefficientforNewtoniananddragreductionflowsinallstates(laminar,transitional,turbulent)andinallregions(smooth,transitional,rough)aretheoreticallydiscussedindetail.Generallawsforlaminarandturbulentflowsobtainedbytheauthorareverifiedbytheexperimentalresultsobtainedbyothers,andthereisgoodagreementbetweenthem.

简介：Inapreviouspaper,amethodhasbeendevelopedtostudythestabilitycharacteristicsoflaminarboundarylayersovercompliantwalls.Inthispaper,theeffectofdoublelayeredcompliantwallandKramertypecompliantwallondelayingthetransitionisinvestigated,anditisshownthattheredoesexistthepossibilitytode-laythetransitionbyapplyingsuchcompliantwalls.

简介：Thestabilitycharacteristicsoflaminarboundarylayersovercompliantwallswasstudiedbythelineartheory.Unlikethepreviousauthors,thecoupledmotionofthefluidandsolidwasrequiredtosat-isfythecontinuityconditionsofboththevelocityandstressattheinterface.Resultsofcalculationsshowthatasthespeedratioordensityratioexceedsacertainthresholdvalue,thetwotypesofunstablewaveswillnolongerbedistinguishable,andthetangentialcomponentofthedisturbancestressisnolongernegligi-ble.Sotheneglectofit,asthepreviousauthorsdid,isunjustified.

简介：Aprogramincorporatingtheparallelcodeoflargeeddysimulation(LES)andparticletransportationmodelisdevelopedtosimulatethemotionofparticlesinanatmosphericturbulentboundarylayer(ATBL).Amodelofparticlesof100-micrometerordercouplingwithlargescaleATBLisproposed.Twotypicalcasesarestudied,onefocusesontheevolutionofparticleprofileintheATBLandthelandingdisplacementofparticles,whereastheotheronthemotionofparticlestream.

简介：Thegenerationandevolutionofturbulentspotsintheopen-channelflowaresimulatednumericallybyusingtheNavier-Stokesequations.Aneffectivenumericalmethodwithhighaccuracyandhighresolutionisdeveloped.Thefourth-ordertimesplittingmethodswithhighaccuracyisproposed.Three-dimensionalcouplingdifferencemethodsarepresentedforthespatialdiscretizationofthePoissonequationofpressureandHemholtzequationsofvelocity,therefore,thefourth-orderthree-dimensionalcouplingcentraldifferenceschemesareconstituted.Thefourth-orderexplicitupwind-biasedcompactdifferenceschemesaredesignedtoovercomethedifficultyforthegeneralhigher-ordercentraldifferenceschemewhichisinadaptableintheboundaryneighborhood.Theiterativealgorithmandoveralltimemarchingisusedtoenhanceefficiency.Themethodisappliedinthenumericalsimulationofturbulentspotsatvariouscomplexboundaryconditionsandflowdomains.Thegenerationandthedevelopingprocessofturbulentspotsaregiven,andthebasiccharacteristicsofturbulentspotsareshownbysimulatingtheevolutionofthewallpulseininclinedopen-channelflow.

简介：Thispaperreviewssomeoftheprincipaluses,overalmostsevendecades,ofcorrelations,inbothEulerianandLagrangianframesofreference,ofpropertiesofturbulentflowsatvariablespatiallocationsandvariabletimeinstants.Commonlycalledspace–timecorrelations,theyhavebeenfundamentaltotheoriesandmodelsofturbulenceaswellasfortheanalysesofexperimentalanddirectnumericalsimulationturbulencedata.

简介：Thechangesofthedevelopingturbulentflowcharacteristicsincurvedductafteraddingabafflearestudiednumericallyatthebody-fittedcoordinates.ak-εmodelisusedtorepresenttheturbulence.acurvedductofrectangularcross-sectioniscomputedfirstly,ithasbeenobservedthatthepredictionsusingtheprocedureagreeverysatisfactorywiththeexperimentaldata.Then,twokindsofsquareductsarestudied,oneisnormalcurvedduct,theotherisaductwithabaffle.Thecomputationalresultsarepresentedandcomparedtoeachother,inordertodisplaythechangesoftheflowafteraddingabaffleincurvedducts.Thesecondaryflowinaductwithabaffleischaracterizedbyfour-vorticesstructurewiththeoutertwobiggerthantheinnertwo.Besides,comparedwiththeductwithoutabaffle,theintensityofthesecondaryflowsisreduced,whichresultsintheflowfieldofthecross-sectionmuchmoreequableandhasmuchmoresignificantmeaningintheengineering.

简介：Granularmaterialsexhibitabundantdissipationsduetofluctuationsinbothgranularmotionsandconfigurations(i.e.,granularskeleton)evolutions.TwingranulartemperaturesTkandTeareintroducedaccountingfortwotypesoffluctuations,andtheso-calledtwingranulartemperaturestheoryisestablishedasanextensionofgranularsolidhydrodynamics.Byusingsimulations,thenonaffinedeformationsina2Dassemblyaresimulatedbyusingdiscreteelementmethods.Byanalogizingwithmicrodamagesindeformedsolids,doublescalardamagevariables,DPandDq,areproposedtodescribethedeformedgranularsolidundertriaxialcompressions.GranularflowsarefoundintrinsicallyturbulentduetothepresenceofTkandtheNaiver-Stokesequationisobtainedforgranularflows.

简介：Accuratepredictionofunsteadyseparatedturbulentflowsremainsoneofthetoughesttasksandapracticalchallengeforturbulencemodeling.Inthispaper,a2DflowpastacircularcylinderatReynoldsnumber3,900isnumericallyinvestigatedbyusingthetechniqueofunsteadyRANS(URANS).Sometypicallinearandnonlineareddyviscosityturbulencemodels(LEVMandNLEVM)andaquadraticexplicitalgebraicstressmodel(EASM)areevaluated.Numericalresultshaveshownthatahigh-performancecubicNLEVM,suchasCLS,aresuperiortotheothersinsimulatingturbulentseparatedflowswithunsteadyvortexshedding.