5358_vortex and drag control mechanism in turbulent flows using riblets Riblets

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1、VortexanddragcontrolmechanisminturbulentflowsusingribletsIntroductionNationalfuelsuseisontherise,soisitssubsidies,whichmakesalargechunkofnationalannualbudgets.Thisstudyconcernswithdragreductioneffortswhichisrelatedtovehiclesefficienciesbywayofaerodynamicseffects.Thestudysupportsnationalagenda

2、ofreducingfuelsuse.Highlyorderedanddirectionalroughsurfaces,knownasribletsalignedintheflowdirectionareknowntoreduceskinfrictionby8-10%.Ribletshavebeenusedonaeroplanestoreducedragswhichnormallyaccountsfor40-50%ofitsfueluse.Ribletshavealsobeenusedasapassiveflowcontroltooli.e.forliftandheattrans

3、ferenhancements,separationdelayandetc.Deceleratingflowsoversmoothsurfacesduetothegeometryofsuchshapesthatcreatesanadversepressuregradient(APG)environmentalsoreducestheskinfriction.Studieshaveshownthatiftheribletswerearrangedintoadivergingandaconvergingdirection(withanangleinthedirectionofthef

4、low),theboundarylayerthickensintheconvergingareasandviceversa.TheeffectsintheconvergingregionissimilartoonecausedbyAPGi.e.reductioninskinfriction.Howeveritisnotknownifthedivergingregionproducestheoppositeeffectsthereforeproducingnonetskinfrictionreduction.Thisstudyseekstounderstandtheroleofri

5、bletsinadivergingandaconvergingdirectioninthepresenceofAPGusingstateoftheart2-dimensionaltraverseandconstanttemperatureanemometer(CTA).TheexperimentsaretobeperformedinAPGturbulentflowswheredivergingandconvergingribletsareappliedontowindtunnel’sfloors.Energyspectrafromthedifferentflowswillbean

6、alyzedtoobservetheeffectsofribletsandAPGindependently,towardsthenear-wallvorticesandtheso-calledlarge-scalesfeaturesinthelogarithmicregion.Itisanticipatedthattheaviation,themaritime,sportingequipment&gearsandautomotiveindustriestobenefitfromsuchfindings.Thelatter,wherelocaluniversitieshaverea

7、dy-accesstoconductcollaborativeresearchdirectlybenefittheaerodynamicssections.Lostduetoaerodynamiceffectsaccountsforapproximately20%oftheenergyforatypicalpassengervehicle,makingitmoreimportantthanothermethodsaimedatreducingfuelssuchaswallosci