IranC2112012ElsevierLtd.Allrightsreserved.applying)andlesssusceptibletobrakefade,whichlargelycontributedtotheirpopularity1.Thethermalanalysisofbrakediscsisaprimarystageinthestudyofthebrakesystems；becausethetemperaturedeterminesthermo-mechanicalbehaviorofthestructure.Inthebrakingsurface,hightemperaturesandthermalgradientsareproduced.Thisgeneratesstressanddeformationsinxstructureofeinthelocalheattransfercoefcientdistribution.Therefore,assumingaconstantvalueforheattransfercoefcientdoesnotseemtobelogical.Inthispaper,thermalanalysisofthewheel-mountedbrakediscR920KfortheER24PClocomotivewhichismanufacturedinMAPNALocomotiveEngineeringandManufacturingCompany(MLC)incooperationwithSIEMENSAGisinvestigated.DrivingforceofER24PCLocoissuppliedusingadiesel-electricenginewiththemaximumspeedof160km/h.Thislocomotiveisusedtopullthepassengerwagons.Forcalculatingtheheattransfercoefcient,*Correspondingauthor.Tel.:989197481360；fax:982188013029.ContentslistsavailableatAppliedThermalEngineering51(2013)948e952E-mailaddress:Behnam.ghadimiut.ac.ir(B.Ghadimi).brakesinmanydifferenttypesofvehicles.Severaladvantagesofbrakediscsovershoesbrakesarereported,includingbetterstop-pingperformance(disccooledreadily),easy-to-control(notself-calculationsinbrakediscs5,12,13.Asitisreportedintheexperimentalresults,CompletheventilatedtypebrakedisccausesagreatchangAsthespeedrestrictionoftrainscontinuestoexpand,over-heatingandthermaldeformationonbrakesystemsaregoingtobecriticalforemergencybraking.Evenifdynamicbrakingsystemsareusedinnormalservicebraking,theirperformancesarenotsuf-cienttoensureanemergencybrakingathighspeed.Sofrictionbrakingsystemshavecrucialroleinemergencybraking.Forseveralyears,brakediscsincreasinglybecamemorepopularthanshoestransferonthetotalamountofdissipatedenergytothesurroundisinsignicant3e7,andconductionandconvectionmodesofheattransferplayacrucialroleincontributionofheatexchangeofthebrakesystem.TheproblemoftheuidowbetweenthensoftheventilatedtypeofbrakediscsisoftenanalyzedinindividualstudiesbasedontheCFDmethod8e11.Neverthelessoftenanaverage,constantvalueoftheheattransfercoefcientisusedattemperature1.Introductionwhichtheconsequencesaremanifestedbytheappearanceofcracks2.Duringthenormalbraking,inuenceoftheradiationheatarticleinfoArticlehistory:Received17September2012Accepted29October2012Availableonline7November2012Keywords:Wheel-mountedbrakediscPadHeattransferLocomotive1359-4311/$eseefrontmatterC2112012ElsevierLtd./10.1016/j.applthermaleng.2012.10.05abstractInrecentdecadestheimprovementofthebrakingperformancesarerequiredduetohighspeedoftrains.Thegeneratedfrictionalheat,duringbrakingoperationcausesseveralnegativeeffectsonthebrakesystemsuchasbrakefade,prematurewear,thermalcracksanddiscthicknessvariation.Itisthenimportanttodeterminethetemperatureeldofthebrakedisc.Inthepresentwork,thermalanalysisofthewheel-mountedbrakediscR920KfortheER24PClocomotiveisinvestigated.Thebrakediscanduidzonearesimulatedasa3Dmodelwithathermalcouplingboundarycondition.Thebrakingprocessissimulatedinlaboratoryandtheexperimentaldataareusedtoverifythesimulationresults.Duringthebraking,themaximumtemperaturewasobservedinthemiddleofbrakingprocessinsteadofthebrakingendpoint.Moreover,alargelaggingwasobservedfornstemperaturewhichrendersnocoolingatthebeginningofthebraking.Discsurfacetemperaturesincreasedbrakingtime,andthendecreased.Laggingeffectrendersnocoolingatthebeginningofthebraking.withincreasingThermalanalysisoflocomotivewheel-mountedB.Ghadimia,*,F.Kowsarya,M.KhoramibaSchoolofMechanicalEngineering,CollegeofEngineering,UniversityofTehran,Tehran,bMechanicalEngineeringDepartment,MAPNALocomotiveCompany,Karaj,IranhighlightsAteachtimestepthelocalHTCwascalculated,andusedfordiscthermalNumericalresultscomparewellwithexperimentaldata.AppliedThermaljournalhomepage:www.elseviAllrightsreserved.1brakediscanalysis.SciVerseScienceDirectE/locate/apthermengparts.Ifthelocomotivestopscompletely(V2u20)thenalltherotatingpartswillbeexpressedrelativetotherevolutionsofthewheel.Eq.(1)canberewrittenasfollowsEb12m1IR2wm!V2112kcfmV21(2)ywheelmassesandassemblyoflocowheel.lEngineering51(2013)948e952949theuidowwithinthechannelwasmodeledusingtheFLUENTCFDsoftware.Ateachtimestep,duetothelocomotivespeedandtemperaturedistributioninthebrakedisc,thelocalheattransfercoefcientofnswascalculatedandwasappliedasaboundaryconditionforthebrakediscthermalanalysis.Anexperimentaldataveriedthemodelingresults.2.ExperimentalsetupArailwaybrakediscsystemistestedontheZF-Dynamometer(Fig.1)intheFaiveleyTransportCompanyandresultswerere-portedtoMLC14.ZF-Dynamometerisabletorunwithspecicmissionprolesindryandwetconditions.Thedynamometerhasanelectricmotorof536kWanduptofourcoupleableywheelmassestosimulatevariousweightsandloadsofvehicles.Themeasurementoftemperatureisaveryimportantstepinthetestprocedure.Forthispurpose,aKTypeThermocouplein1.5mmthicknesswasused.Formodelingthebrakingphenomena,loco-motivewheelwasacceleratedwiththeconstantvalueof0.8m/s2andreachedtothedesiredvelocity,thenthebrakingstartedandcausedconstantdecelerationwiththerateof1.117m/s2.Duringthebraking,brakingsurfaceandnswalltemperatureswererecordedandusedforvalidatingthenumericalresults.3.ModelingTheER24PClocomotiveconsistsoftwobogies.Eachbogiehasfourwheelswithonesetofwheel-mountedbrakediscswhichconsistsoftwobrakediscsarrangedonbothsidesofawheelandareboltedtogetherthroughthewheelweb(Fig.2).3.1.ThermalmodelingRegardingtotheuniformpressureortheconstantwearFig.1.ZF-dynamometerwithcoupleableB.Ghadimietal./AppliedThermaboundaryconditionatthecontactsurface,twomethodsareavail-ableforcalculatingthebrakingheatgenerationrate.Uniformpressuredistributioninthecontactregionisoftenvalidwhenthepadisnew.Howeverafterbrakingforseveraltimes,assumptionofuniformwearismorepragmatic.Inthisstudy,thepadwasusedseveraltimesanduniformwearbetweenpadandbrakediscisstabilized,hencetheheatuxisjustafunctionoftimeanditisindependenceofthespatialvariables5.ForavehiclewhichisdeceleratingonalevelsurfacefromahighervelocityV1toalowervelocityV2thebrakingenergyEbcanbewrittenasEb12mC16V21C0V22C1712IC16u21C0u22C17(1)whereIisrelatedtothemassmomentofinertiaoftherotatingparts,mlocomotivemassanduistheangularvelocityofrotatingFig.2.(a)Wheel-mountedbrakedisc,(b)wheel-mountedbrakediscR920K,set,mounted.wherelistheheatgenerationratio,q00dandq00paretheheatuxabsorbedbythebrakedisc,andpad,rrepresentsdensity,Cisthespecicheat,kthethermalconductivityandtheindexdandpindicatediscandpad,respectively.UsingEq.(4)and(5),theheatTable1BrakediscR920Kdata.Brakingmassperbrakedisc(kg)5456.5Wheeldiameterorigin(mm)1100Brakediscouterdiameter(mm)920Brakediscinnerdiameter(mm)640Widthofring(mm)24Widthofns(mm)30Densityofbrakediscmaterial(kg/m3)7246Specicheatofbrakediscmaterial(J/kgK)500Thermalconductivityofbrakediscmaterial(W/mK)58Densityofbrakepad(kg/m3)2180Specicheatofbrakepad(J/kgK)1090Thermalconductivityofbrakepad(W/mK)1.67Averagefrictioncoefcient(m)0.32Ambienttemperature(C14C)55Starttemperatureofbrakedisc(C14C)55Decelerationofvehicle(average)(m/s2)1.177Engineering51(2013)948e952B.Ghadimietal./AppliedThermal950wherekcfisthecorrectionfactorforrotatingmassesandRwisthewheelradius.BrakingpowerPbisequaltobrakingenergydividedbythebrakingtimet,orPbdEbdt(3)Forconstantdeceleration,Eq.(2)andEq.(3)yieldthebrakepowerasPbkcfmaV1C0at(4)whereaisthedecelerationofthelocomotive.Thedistributionofbrakingenergybetweenpadanddisccannotbepredictedreadily.Generally,thermalconductivityofthebrakepadsissmallerthanthedisc(kpkd),soonecanconsiderthatthetotalamountofthebrakingheatwillbecompletelyabsorbedbythebrakedisc.Thisassumptionleadstohighertemperatureestimationforbrakedisc.Toavoidthisissue,supposethatthebrakingoper-ationtimeisshort,hencethepadandbrakecanbeconsideredassemi-innitesolidsandtheheatgenerationratiocanbecalculatedasfollows15lq00dq00prdCdkdrpCpkp!1=2(5)Fig.3.Meshconstruction,a)brakedisc,b)uidregion.uxonthebrakingsurfacecanbefoundq00dlAl1kcfmaV1C0at(6)whereAisthediscandpadcontactarea.3.2.ModelingandboundaryconditionsForFEMandCFDanalysis,three-dimensional(3D)constructionsofbrakediscandcoolingairdomainweremodeled(Fig.3).Forsolvingthecontinuity,momentumandenergyequations,FLUENTunsteadysolverwasusedwithSIMPLEalgorithmforpressureandvelocitycouplingandkC0realizablemodelforviscousowmodeling.PhysicalpropertiesofbrakediscandboundaryconditionsforanalysisaregiveninTable1.HeatuxinthebrakingsurfaceiscalculatedfromEq.(6).Ateachtimestep,accordingtotheloco-motivespeedanddistributionoftemperatureinthebrakedisc,theFig.4.ThermalsimulationofbrakediscR920K,onestopsfrom154km/h.lEngineering51(2013)948e952951B.Ghadimietal./AppliedThermalocalheattransfercoefcientofnsiscalculatedbysolvingtheRANSandEnergyequationsintheuidzone,andusedasaboundaryconditionforthebrakediscthermalanalysis.Thentheenergyequationwassolvedinthebrakediscandtemperaturedistributionatthesubsequenttimestepwascalculated.Thisprocedurecontinuesuntilthelocomotivecametoastop.4.ResultsanddiscussionThethermalanalysisofwheelmountedbrakediscofMAPNALocoER24PCwasconducted,inthecaseofoneemergencystopfrom154km/h.Fig.4showsnumericalresultsingoodcomparisonwithexperimentaldata.Fromthisgure,itisseenthatthediscsurfacetemperaturewillincreasewithincreasingbrakingtimeandthenitdecreasesduetoasignicantreductioninheatgenerationvalueoverthebrakesurface.Duetotheheatconductioneffects,itispossibletoseealargedelayortimelaginnstemperature.Thislaggingeffectrendersnocoolingatthebegin-ningofthebraking,sothesurfacetemperaturewillincreasesharply.Afterafewseco