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IranC2112012ElsevierLtd.Allrightsreserved.applyingandlesssusceptibletobrakefade,whichlargelycontributedtotheirpopularity[1].Thethermalanalysisofbrakediscsisaprimarystageinthestudyofthebrakesystems;becausethetemperaturedeterminesthermo-mechanicalbehaviorofthestructure.Inthebrakingsurface,hightemperaturesandthermalgradientsareproduced.Thisgeneratesstressanddeformationsinxstructureofeinthelocalheattransfercoefficientdistribution.Therefore,assumingaconstantvalueforheattransfercoefficientdoesnotseemtobelogical.Inthispaper,thermalanalysisofthewheel-mountedbrakediscR920KfortheER24PClocomotivewhichismanufacturedinMAPNALocomotiveEngineeringandManufacturingCompanyMLCincooperationwithSIEMENSAGisinvestigated.DrivingforceofER24PCLocoissuppliedusingadiesel-electricenginewiththemaximumspeedof160km/h.Thislocomotiveisusedtopullthepassengerwagons.Forcalculatingtheheattransfercoefficient,*Correspondingauthor.Tel.989197481360;fax982188013029.ContentslistsavailableatAppliedThermalEngineering512013948e952E-mailaddressBehnam.ghadimiut.ac.irB.Ghadimi.brakesinmanydifferenttypesofvehicles.Severaladvantagesofbrakediscsovershoesbrakesarereported,includingbetterstop-pingperformancedisccooledreadily,easy-to-controlnotself-calculationsinbrakediscs[5,12,13].Asitisreportedintheexperimentalresults,CompletheventilatedtypebrakedisccausesagreatchangAsthespeedrestrictionoftrainscontinuestoexpand,over-heatingandthermaldeformationonbrakesystemsaregoingtobecriticalforemergencybraking.Evenifdynamicbrakingsystemsareusedinnormalservicebraking,theirperformancesarenotsuffi-cienttoensureanemergencybrakingathighspeed.Sofrictionbrakingsystemshavecrucialroleinemergencybraking.Forseveralyears,brakediscsincreasinglybecamemorepopularthanshoestransferonthetotalamountofdissipatedenergytothesurroundisinsignificant[3e7],andconductionandconvectionmodesofheattransferplayacrucialroleincontributionofheatexchangeofthebrakesystem.TheproblemofthefluidflowbetweenthefinsoftheventilatedtypeofbrakediscsisoftenanalyzedinindividualstudiesbasedontheCFDmethod[8e11].Neverthelessoftenanaverage,constantvalueoftheheattransfercoefficientisusedattemperature1.Introductionwhichtheconsequencesaremanifestedbytheappearanceofcracks[2].Duringthenormalbraking,influenceoftheradiationheatarticleinfoArticlehistoryReceived17September2012Accepted29October2012Availableonline7November2012KeywordsWheel-mountedbrakediscPadHeattransferLocomotive1359-4311/eseefrontmatterC2112012ElsevierLtd.http//dx.doi.org/10.1016/j.applthermaleng.2012.10.05abstractInrecentdecadestheimprovementofthebrakingperformancesarerequiredduetohighspeedoftrains.Thegeneratedfrictionalheat,duringbrakingoperationcausesseveralnegativeeffectsonthebrakesystemsuchasbrakefade,prematurewear,thermalcracksanddiscthicknessvariation.Itisthenimportanttodeterminethetemperaturefieldofthebrakedisc.Inthepresentwork,thermalanalysisofthewheel-mountedbrakediscR920KfortheER24PClocomotiveisinvestigated.Thebrakediscandfluidzonearesimulatedasa3Dmodelwithathermalcouplingboundarycondition.Thebrakingprocessissimulatedinlaboratoryandtheexperimentaldataareusedtoverifythesimulationresults.Duringthebraking,themaximumtemperaturewasobservedinthemiddleofbrakingprocessinsteadofthebrakingendpoint.Moreover,alargelaggingwasobservedforfinstemperaturewhichrendersnocoolingatthebeginningofthebraking.Discsurfacetemperaturesincreasedbrakingtime,andthendecreased.Laggingeffectrendersnocoolingatthebeginningofthebraking.withincreasingThermalanalysisoflocomotivewheel-mountedB.Ghadimia,*,F.Kowsarya,M.KhoramibaSchoolofMechanicalEngineering,CollegeofEngineering,UniversityofTehran,Tehran,bMechanicalEngineeringDepartment,MAPNALocomotiveCompany,Karaj,IranhighlightsAteachtimestepthelocalHTCwascalculated,andusedfordiscthermalNumericalresultscomparewellwithexperimentaldata.AppliedThermaljournalhomepagewww.elseviAllrightsreserved.1brakediscanalysis.SciVerseScienceDirectEngineeringer.com/locate/apthermengparts.IfthelocomotivestopscompletelyV2u20thenalltherotatingpartswillbeexpressedrelativetotherevolutionsofthewheel.Eq.1canberewrittenasfollowsEb12m1IR2wmV2112kcfmV212flywheelmassesandassemblyoflocowheel.lEngineering512013948e952949thefluidflowwithinthechannelwasmodeledusingtheFLUENTCFDsoftware.Ateachtimestep,duetothelocomotivespeedandtemperaturedistributioninthebrakedisc,thelocalheattransfercoefficientoffinswascalculatedandwasappliedasaboundaryconditionforthebrakediscthermalanalysis.Anexperimentaldataverifiedthemodelingresults.2.ExperimentalsetupArailwaybrakediscsystemistestedontheZF-DynamometerFig.1intheFaiveleyTransportCompanyandresultswerere-portedtoMLC[14].ZF-Dynamometerisabletorunwithspecificmissionprofilesindryandwetconditions.Thedynamometerhasanelectricmotorof536kWanduptofourcoupleableflywheelmassestosimulatevariousweightsandloadsofvehicles.Themeasurementoftemperatureisaveryimportantstepinthetestprocedure.Forthispurpose,aKTypeThermocouplein1.5mmthicknesswasused.Formodelingthebrakingphenomena,loco-motivewheelwasacceleratedwiththeconstantvalueof0.8m/s2andreachedtothedesiredvelocity,thenthebrakingstartedandcausedconstantdecelerationwiththerateof1.117m/s2.Duringthebraking,brakingsurfaceandfinswalltemperatureswererecordedandusedforvalidatingthenumericalresults.3.ModelingTheER24PClocomotiveconsistsoftwobogies.Eachbogiehasfourwheelswithonesetofwheel-mountedbrakediscswhichconsistsoftwobrakediscsarrangedonbothsidesofawheelandareboltedtogetherthroughthewheelwebFig.2.3.1.ThermalmodelingRegardingtotheuniformpressureortheconstantwearFig.1.ZF-dynamometerwithcoupleableB.Ghadimietal./AppliedThermaboundaryconditionatthecontactsurface,twomethodsareavail-ableforcalculatingthebrakingheatgenerationrate.Uniformpressuredistributioninthecontactregionisoftenvalidwhenthepadisnew.Howeverafterbrakingforseveraltimes,assumptionofuniformwearismorepragmatic.Inthisstudy,thepadwasusedseveraltimesanduniformwearbetweenpadandbrakediscisstabilized,hencetheheatfluxisjustafunctionoftimeanditisindependenceofthespatialvariables[5].ForavehiclewhichisdeceleratingonalevelsurfacefromahighervelocityV1toalowervelocityV2thebrakingenergyEbcanbewrittenasEb12mC16V21C0V22C1712IC16u21C0u22C171whereIisrelatedtothemassmomentofinertiaoftherotatingparts,mlocomotivemassanduistheangularvelocityofrotatingFig.2.aWheel-mountedbrakedisc,bwheel-mountedbrakediscR920K,set,mounted.wherelistheheatgenerationratio,q00dandq00paretheheatfluxabsorbedbythebrakedisc,andpad,rrepresentsdensity,Cisthespecificheat,kthethermalconductivityandtheindexdandpindicatediscandpad,respectively.UsingEq.4and5,theheatTable1BrakediscR920Kdata.Brakingmassperbrakedisckg5456.5Wheeldiameteroriginmm1100Brakediscouterdiametermm920Brakediscinnerdiametermm640Widthofringmm24Widthoffinsmm30Densityofbrakediscmaterialkg/m37246SpecificheatofbrakediscmaterialJ/kgK500ThermalconductivityofbrakediscmaterialW/mK58Densityofbrakepadkg/m32180SpecificheatofbrakepadJ/kgK1090ThermalconductivityofbrakepadW/mK1.67Averagefrictioncoefficientm0.32AmbienttemperatureC14C55StarttemperatureofbrakediscC14C55Decelerationofvehicleaveragem/s21.177Engineering512013948e952B.Ghadimietal./AppliedThermal950wherekcfisthecorrectionfactorforrotatingmassesandRwisthewheelradius.BrakingpowerPbisequaltobrakingenergydividedbythebrakingtimet,orPbdEbdt3Forconstantdeceleration,Eq.2andEq.3yieldthebrakepowerasPbkcfmaV1C0at4whereaisthedecelerationofthelocomotive.Thedistributionofbrakingenergybetweenpadanddisccannotbepredictedreadily.Generally,thermalconductivityofthebrakepadsissmallerthanthedisckpkd,soonecanconsiderthatthetotalamountofthebrakingheatwillbecompletelyabsorbedbythebrakedisc.Thisassumptionleadstohighertemperatureestimationforbrakedisc.Toavoidthisissue,supposethatthebrakingoper-ationtimeisshort,hencethepadandbrakecanbeconsideredassemi-infinitesolidsandtheheatgenerationratiocanbecalculatedasfollows[15]lq00dq00prdCdkdrpCpkp125Fig.3.Meshconstruction,abrakedisc,bfluidregion.fluxonthebrakingsurfacecanbefoundq00dlAl1kcfmaV1C0at6whereAisthediscandpadcontactarea.3.2.ModelingandboundaryconditionsForFEMandCFDanalysis,three-dimensional3DconstructionsofbrakediscandcoolingairdomainweremodeledFig.3.Forsolvingthecontinuity,momentumandenergyequations,FLUENTunsteadysolverwasusedwithSIMPLEalgorithmforpressureandvelocitycouplingandkC0εrealizablemodelforviscousflowmodeling.PhysicalpropertiesofbrakediscandboundaryconditionsforanalysisaregiveninTable1.HeatfluxinthebrakingsurfaceiscalculatedfromEq.6.Ateachtimestep,accordingtotheloco-motivespeedanddistributionoftemperatureinthebrakedisc,theFig.4.ThermalsimulationofbrakediscR920K,onestopsfrom154[km/h].lEngineering512013948e952951B.Ghadimietal./AppliedThermalocalheattransfercoefficientoffinsiscalculatedbysolvingtheRANSandEnergyequationsinthefluidzone,andusedasaboundaryconditionforthebrakediscthermalanalysis.Thentheenergyequationwassolvedinthebrakediscandtemperaturedistributionatthesubsequenttimestepwascalculated.Thisprocedurecontinuesuntilthelocomotivecametoastop.4.ResultsanddiscussionThethermalanalysisofwheelmountedbrakediscofMAPNALocoER24PCwasconducted,inthecaseofoneemergencystopfrom154km/h.Fig.4showsnumericalresultsingoodcomparisonwithexperimentaldata.Fromthisfigure,itisseenthatthediscsurfacetemperaturewillincreasewithincreasingbrakingtimeandthenitdecreasesduetoasignificantreductioninheatgenerationvalueoverthebrakesurface.Duetotheheatconductioneffects,itispossibletoseealargedelayortimelaginfinstemperature.Thislaggingeffectrendersnocoolingatthebegin-ningofthebraking,sothesurfacetemperaturewillincreasesharply.Afterafewseconds,theheatfluxaffectsthefinsandfinstemperatureincreases.Byconvectioncoolingofthefins,brakingheatdissipatestotheair,andtherateofincreasinginsurfacetemperaturewillbereduced.TemperaturedistributiononthebrakediscinthreedifferenttimesispresentedinFig.5.Duetonon-uniformcoolingofthefinsintheirlength,themaximumtemperaturewasobservedinthedifferentregionsinthedifferenttimes.FromFig.5itisobviousthatthetemperaturevalueatthetopofthefinsisgreaterthanthetemperaturevaluebetweenthefins.Toelaboratethisbehavior,thedistributionofvelocityvectoratt20.5sispresentedinFig.6.LinearandrotationalvelocityeffectsFig.5.Temperaturedistributionsoftheontheairflowthroughthediscareclearlyvisibleinthisfigure.Stagnationandwakeregionregionaatthetopofthefins,andhighairvelocityabout22m/scanbeseenbetweenthefinsregionb.Stagnationregioncausedlowlocalheattransfercoefficientatregiona,whichleadstoareductioninheattransferanditcausesahighertemperaturevalue.Additionally,higherairvelocitybetweenthefinsleadstohighheattransfercoefficientbrakediscatdifferenttimes.Fig.6.Velocityvectordistributionatt20.5s.
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