简介：Alargediamondcrystalupto500μmindiameterwithasmooth(100)facetatitstophasbeensynthesizedonMosubstratethroughmicrowaveplasmachemicalvapordeposition(MPCVD).Itsmorphologyandqualitywerecharacterizedbyscanningelectronmicroscopy(SEM),andthegrowthmechanismwasroughlyillustratedfrombothmacroscopicandmicroscopicviewpoints.Itwasfoundthatmorphologicalinstabilitiesareamajorfactorresultinginsynthesisoflargediamondcrystals,moreover,highmicrowavepowerdensity(MPD),highCH4concentrations,highpressure,highsubstratesurfacetemperatureandtheadditionofasmallamountofO2werealsonecessaryforthesynthesisoflargediamondcrystals.

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.

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