简介：Glowdischargeisintroducedasanartificialdisturbancetoinvestigatetheevolutionoffirst-andsecond-modeinstabilitiesinahypersonicflatplateboundarylayer.ExperimentsareconductedinaMach6.5quietwindtunnelusingRayleighscatteringvisualizationandparticleimagevelocimetry(PIV).Detailedanalysisoftheexperimentalobservationsisprovided.Itisfoundthattheartificiallyintroduced17kHzdisturbance,whichbelongstothefirst-modefrequencyband,caneffectivelyenhancefirst-modewaves.Moreover,itcanenhancesecond-modewavesevenmoreintensely.Possiblemechanismstoexplainthisphenomenonarediscussed.

简介：AnartificialdisturbanceisintroducedintotheboundarylayeroveraflatplatetoinvestigatetheeffectonthetransitionprocessintheMach6.5windtunnelatPekingUniversity.Alinearstabilitytheory(LST)isutilizedtopredicttheevolutionoftheeigenmodes,andthefrequencyoftheartificialdisturbanceischosenaccordingtotheLSTresults.Theartificialdisturbanceisgeneratedbyglowingdischargeonthesurfaceoftheplateclosetotheleadingedge.TheRayleigh-scatteringvisualizationandparticleimagevelocimetry(PIV)measurementsareperformed.Bycomparingtheexperimentalresultswithartificialdisturbanceswiththoseunderthenaturalcondition(withoutartificialdisturbances),thepresentpapershowsthatthesecond-modeinstabilitywavesaresignificantlystimulatedbytheartificialdisturbances,andtheboundarylayertransitioniseffectivelytriggered.

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

简介：Itisaverydifficulttasktodevelopamethodofreducingturbulentboundarylayerdrag.However,inrecentyears,plasmaflowcontroltechnologyhasdemonstratedhugepotentialinfrictiondragreduction.Tofurtherinvestigatethisissue,asmoothplatemodelwasdesignedasatestingobjectarrangedwithabidirectionaldielectric-barrier-discharge(DBD)plasmaactuator.Inaddition,measurementofskinfrictiondragwasachievedbyapplyinghotwireanemometrytoobtainthevelocitydistributionoftheturbulentboundarylayer.AmethodofquantifyingthefrictiondrageffectwasadoptedbasedontheSpaldingformulafittedwiththeexperimentdata.Whenplasmaactuationwasconducted,avelocitydefectoccurredatthetwomeasuringpositions,comparedwiththenoplasmacontrolcondition;thismeansthattheDBDplasmaactuationcouldreducethedragsuccessfullyinthedownstreamoftheactuator.Moreover,dragreductioncausedbybackwardactuationwasslightlymoreefficientthanthatcausedbyforwardactuation.Withanincreasingdistancefromplasmaactuation,thedrag-reductioneffectcouldbecomeweaker.Experimentalresultsalsoshowthattheimprovementofdrag-reductionefficiencyusingaDBDplasmaactuatorcanachieveabout8.78%inthelocalregionoftheexperimentalflatmodel.

简介：Thesuppressionoftherecombinationofelectronsandholes(e–h)andtheenhancementofthelightabsorptionofsemiconductorsaretwokeypointstowardefficientphotocatalyticdegradation.Here,wereportafew-layerg-C3N4/α-MoO3nanoneedles(flg-C3N4/α-MoO3NNs)all-solid-stateZ-schememechanismphotocatalystsynthesizedviaatypicalhydrothermalmethodinacontrolledmanner.Therecombinationofthephoto-inducede–hpairscouldbeeffectivelyrestrainedbytheZ-schemepassagewaybetweentheflg-C3N4andα-MoO3NNsinthecomposite,whichcouldalsopromiseahighredoxabilitytodegradepollutants.Anditbecamepossibleforthepreparedphotocatalysttoabsorblightinawiderangeofwavelengths.Thedetailedmechanismwasstudiedbyelectronspin-resonancespectroscopy(ESR).Thelow-dimensionalnanostructureofthetwoconstituents(α-MoO3NNswithone-dimensionalstructureandflg-C3N4withtwo-dimensionalstructure)endowedthecompositewithvarietiesofexcellentphysicochemicalproperties,whichfacilitatedthetransferanddiffusionofthephotoelectronsandincreasedthespecificsurfaceareaandtheactivesites.The10wt%flg-C3N4/α-MoO3NNsshowedthebestphotocatalyticperformancetowardRhBdegradation,therateofwhichwas71.86%,~2.6timeshigherthanthatofα-MoO3NNs.