天津地铁站气流组织的数学模拟_英文_

1、TransactionsofTianjinUniversityVol.8No.4 Dec.2002NumericalSimulationofAirDistributionforTianjinSubwayStation*WANGLiang2zhu1,WANGLai2,TUGuang2bei1(1.SchoolofEnvironmentalScienceandEngineering,TianjinUniversity,Tianjin300072,China;2.SchoolofSciences,TianjinUniversity,Tianjin300072,China)Abstract:Inreb

2、uildingTianjinMetro,numericalsimulationsareperformedtoevaluatetheoriginaldesignoftheventilationsystemofSouthwestStationandanewsystemisgiventooptimizethevelocityandtemperaturefieldsatthestation.Fieldmeasurementsareconductedtovalidatetheturbulencemodelandacquireboundarycondi2tions.Thesimulationresultt

3、allieswithtestingdataonthesportthatisfoundthattwo2equationturbulencemodelisacceptableinsimulatingcomplexflowatthestation.Amethodofsimplifyingthesimulationofthetransientflowatthestationintosteadyflowisusedandthevalidationcriterionforthissimulationisalsogiven.Keywords:Computationalfluiddynamics(CFD);f

4、ieldmeasurements;turbulencemodel;subwaystationSubwayhasbeenapowerfultoolforurbantrans2portationsince1863whentheLondonUnderground,thefirstsubwaysystem,beganserviceinLondon,England.WiththeincreasingpopulationandthegreatlydevelopingeconomyofChina,subwayisplayingmoreandmoreim2portantrole.TianjinMetro,th

5、esecondlybuiltsubwayinChina,isgoingtoberebuilttomeetthedemandoflocalurbandevelopmentandexpectedtobeavailableforBeijing2008OlympicGames.X1 DefinitionofproblemAlthoughdifferentexistentstationsofTianjinMetrohavedifferentstructuresandgeometries,theSouthwestStationisthemosttypicalone.Itsgeometryisshownin

6、Fig.1.Theplatformmechanicalventilationisrealizedbytwojetopeningslocatingateachendofstationandthesupplyairjetstowardstrainandtrack.Thereisnome2chanicalexhaustsystematthestationandairisremovedmechanicallybytunnelfansandnaturallybytheexitsofthestation.TheoriginaldesignforrebuildingSouthwestStationissho

7、wninFig.2.ThedesignvolumeflowofSouthwestStationis400 000 m3/h.Formostexistentstations,theplatformheightisonly2.9 m,whichistoolowtosetceilingducts.Sointhisoriginaldesigntherearetwogrilleventsateachendoftheplatformtosupplyfreshairalongtheplatformlengthdirectionandtwogrilleventstojetairbreadthwaystowar

8、dstrains.Thedesignvelocityofeachlengthwaysgrilleventis5.54 m/sandforeachbreadthwaysventitis5.28 m/s.Undertheplatform80grilleventsofthesamedesignvelocity(4.62 m/s,40foreachplatformofthestation)areresponsibleforexhaust. Althoughitrequiresrelativelylittlestructurerebuild2ingofthestationexperientially,t

9、hisdesignseemstohavesomeproblems. 1)Thespeedoflengthwiseventsisupto5.54m/s,whichissogreatthatitmaycauseunbearablespeedatsomepointsoftheplatform. 2)Thelengthwisesuppliedairmaymostlyflowout2sideplatformthroughtheexitssothattheareabetweentwoexitsmaybecome/DeadZone0whereunbearabletem2peraturemaybecaused

10、. Inthispaper,computationalfluiddynamics(CFD)techniquesareusedtoevaluatethevelocityandtempera2turefieldsabovetheplatformandanewventilationsce2nariowithbetterthermalconditionsisthensuggested.Fieldtestsattheexistentstationareperformedtoacquiretheboundaryconditionsforthelatersimulation.2 Precedingsimpl

11、ificationsandpresumptions Becauseofmechanicalventilationandtheexistenceoftrain2drivenwind,theturbulenceontheplatformistran2sientandcomplex.WhileensuringthereliabilityofthecomputationresultssomeprecedingsimplificationsandXAccepteddate:2002206223. WANGLiang2zhu,bornin1979,male,M. *SupportedbytheCommit

12、teeofTianjinUrbanConstruction(No.2001222).TRANSACTIONSOFTIANJINUNIVERSITYVol.8No.42002presumptionshavetobetaken.1)Sincethemaximumairvelocityisreachedattheperiodwhentrainstopatorstartawayfromthestation,theperiodthesimulationconcernsaboutisfromthepointwhenatthesectionof/x=0.0 m0(Fig.1)theairveloc2ityb

13、egintochangeunderpiston2effecttothepointwhentraintotallystopsatthestation(definedasapulling2incy2cle).Thistransientprocessissimplifiedtosteadyprocessinwhichatrainhasstoppedandtheairvelocityoffieldmeasurementsatthesetwoendsofthestation(x=0.0 mandx=74.4 minFig.1.)andthepassengerexits(Fig.1.)areprocess

14、edtobetime2averagedwhenthesevelocityboundaryconditionsforlatersimulationaredeter2mined.(Vexit)isalsothesame.Basedonthispresumptionthere2sultsofthefieldmeasurementsattheexistentstationcanbeusedasvelocityboundaryconditionstopredictvelocityfieldofnewstation.3 Methods3.1 Theory Theflowatthestationistake

15、nasincompressiblesteadyturbulence.Althoughgenerallytheturbulencemodelisnotverysoundtopredictturbulentflow,thevali2dationofthesimulationattheexistentstation(asshowninFig.3)showsthatthismodelcanbeused.ThebasicgoverningequationsaretheMassConservationEquation,MomentumEquation,theTransportationEquationof

16、k,theTransportationandEnergyEquationofE.Fig.1 Existentsouthweststation2)Thevolumeflow(Vpiston)drivenintothestationFig.3 Validationofthesimulationattheexistentbypulling2intrainisdeterminedbysuchfactorsasBRstation(seeFig.1forsectionlocations)(blockingratio,theratiooftraincross2sectionareatotun2nelcros

17、s2sectionarea),thelengthofthetrain(Ltrain)andtheresistanceofstationRstationetc.Forexistentandnew ThegoverningequationsareintegratedonthespatialstationsBRarealmostthesame.AlthoughtheLtrainofthecontrolvolumes.Exceptthatpressureusesbodyforcelatterdoublestheoneoftheformerwhichmayincreaseweightedscheme,o

18、therdependentvariables(momentum,Vpiston,theRstationofthelatterisgreaterthantheoneofkandEetc)usesecond2orderupwindschemeswhentheyarecomputedatthecellfaces.Pressureandvelocityaretheformerwhichmaycounteractthisincrease.Soitispre2sumedthatVpistonisthesameforbothnewandexistentcoupledbySIMPLEAlgorithm.sta

19、tionandthevolumeflowthroughthepassengerexits3.2 FieldmeasurementsAttheexistentSouthwestStationtheMultichannelAnemomasterHotwireAnemoscopeisusedtomeasureairvelocities.Thelayoutofmeasuringpointsandtheloca2tionsofmeasuringsectionsareshowninFig.1.Onceeach2stheanemoscopescansallpointsandautomaticallyprin

20、ttheresults.Alldataarerecordedduringacompletepulling2incycle.Thenthesedataareprocessedtoyieldtime2averagedvelocityofpersection.InfraredThermome2terisusedtomeasurethetemperaturesofthewallsofthestationwhicharetakenastheconstanttemperaturether2malconditionsinthesimulation.Fig.2 Originaldesignforthenews

21、outhweststationTRANSACTIONSOFTIANJINUNIVERSITYVol.8No.420023.3 ComputationandsimulationFull2scalemodelsoftheexistentandnewstationarecreated.Firstly,bytakingtheresultsofthefieldmea2surementsasboundaryconditions,theairvelocitiesoftheexistentplatformarecomputedandthevelocitiesoffieldmeasuringpointsareu

22、sedtovalidatethetwo2equationmodelandthesimulation.SomeboundaryvelocitiesareunmeasurablesuchastheSectionUinFig.1.Sotheflowatthissectionisestimatedbytrialcomputations.Second2ly,theseboundaryconditionsareappliedtothesimulationoftheoriginaldesignofthenewstation.Thenthesug2gestedventilationscenarioiscomp

23、utedunderthesameconditions.Thetemperaturefieldsareonlycomputedinboththeoriginalandthesuggesteddesignatthenewsta2tionbecausetheheatloadattheexistentstationisnottyp2icalanddifficulttobedetermined.Sinceitisimpossibletogetexactvaluesateverypointandallcomputedvelocitiesaretime2averaged,thesimula2tionisac

24、ceptableiftheaveragevelocitiesatcorrespondingcross2sectionsapproachthetime2averagedmeasuredveloci2ties.Thisisthevalidationcriterionofthesimulation. Fig.4 Predictedpointvelocities(y=3.25 m, theoriginaldesign,thenewstation)4 ResultsanddiscussionsFig.3showsthatthetwo2equationmodelandtheprecedingsimplif

25、icationsareacceptableinpredictingflowatthestation.AlthoughthecomputedvelocityatSectionCandEdonctequaltothevaluesofthefieldmeasure2ment,thedifferencesareacceptableandtheoverallvari2ancetrendofthevelocityalongtheplatformagreeswiththemeasurement.Inthesimulationoftheoriginaldesignforthenewstationasshown

26、inFig.4,itisapparentthatattheheightof1.7 mabovetheplatformthevelocityofsomespotsreaches3.57m/swhilebeyondtheexittheairspeedre2ducesto0.35)0.65 m/s.Thiscanbeexplainedbythefactthatmuchofthefreshairdirectlyflowsoutofthesta2tionthroughtheexits.Althoughthevelocityofthezonebetweenthetwoexitsisnottoolowthe

27、ventilationeffi2ciencyoftheoriginaldesignisthusunsatisfactory.Thesimulationalsoshowsthatthemaximumvelocityexistsattheexits,whichagreeswellwiththereferencesandtheexperience.Inthesuggesteddesignattheheightof1.7 mabovetheplatform,themaximumvelocityisonly1.68m/sandtheoverallvelocityfieldisrelativelybala

28、nced(re2fertoFig.5).Thesuppliedairfromthebreadthwaysventsalsoverywellpreventsthehotcontaminatedtrain2drivenairfromspreadingontotheplatform.Althoughtherearestillsomezoneswherethevelocityareonly0.2)0.4 m/stheycanbecompensatedbytheadjacentzoneswherethevelocityishigher.Ontheotherhandthefreshairfromthebr

29、eadthwaysventspassesthroughthepassengers,takesawayheatandhumidity,collectsandisexhaustedbytheunder2platformvents.Theventilationef2ficiencyisquitesatisfactory.Fig.5 Predictedpointvelocities(y=3.25 m, suggesteddesign,thenewstation) Fromthereferences,theheatloadsfromthetraincondenserandthebrakeresistan

30、cerespectivelyareabout320 kWand200 kWwhicharethegreatestheatsources.Frompeopleandlightingtheyare44 kWand30.6 kW.Thetemperatureoffreshair,tunnelairandthestationwallsare27 e,25 eand24 erespec2tively(theoutdoorventilationdesigntemperatureinsum2meris27 eaccordingtothereferences).Undertheabovethermalboun

31、daryconditionsthesimulationsshowthatfortheoriginaldesignthetemperatureontheplat2formisabout32 e)34 eandforthesuggestedde2sign,itisabout28 ewhenthewholestationflowre2mainsthesame.Thedesigntemperatureoftheoriginal)TRANSACTIONSOFTIANJINUNIVERSITYVol.8No.42002systemis30 e.Soitisapparentthatthesuggesteds

32、ystemisalsomuchbetterinsatisfyingthedesignrequire2mentsthantheoriginalone.Sincepassengersmayfeelslightlyuncomfortableat28 ewhentheyenterintothestationfromtheoutsideenvironmentofhighertempera2ture,itisverypromisingtosaveenergyinthesuggesteddesignbyreducingthewholestationflowandincreasingtheplatformte

33、mperature.Technicallythisnewdesignisalsoapplicable.InFig.6undertheplatformtheductwiththecross2sectionof2.0m1.6 misusedforthebreadthwaysventilation.Themaximumairvelocityintheductisabout14m/s,whichisacceptableforbrickductsinsubway.topredicttime2averagedflowatsubwaystation.Thesim2ulationresultsareinflu

34、encedgreatlybytheboundarycon2ditionssuchasboundaryvelocityandpressure.Asforthetransienceoftheairflowattheplatform,itisalsofeasibletosimplifyitintosteadyflowinordertogettime2averagedvelocityfield.Intheabovesimulationthefieldmeasure2mentresultsattheexistentstationareappliedintothesimulationofthenewstation.Itissuggestedthatcarefulanalysisandcomparisonshouldbeconductedtoensuretheapplicabilityofthismethod.Somecorrectionsmaybeusedifnecessary. Thebreadthwayventilationhasmoreadvant