8/31/2015 CentrifugalCompressorDesignandReratinginTurbochargers

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CentrifugalCompressorDesignandReratinginTurbochargersWrittenbyLeonidMoroz

Monday,05April201008:17

LeonidMoroz

SoftInWay,Inc.Burlington,MA01803,USA

SergeyGnezdilovJSCSKBTPenza,440034,Russia

Contactauthor:LeonidMoroz,L.Moroz@SoftInWay.com

Abstract

Specialnumericalresearchiscarriedouttostudytheeffectsofdifferentcentrifugalcompressordesignandreratingstrategiesneededforflowpathcomponentsstandardizationduringmanufacturingandretrofittingprocessesinturbochargers.

Experimentaldatavscalculationresultscomparisonsforseveralcentrifugalcompressordesignsareusedtoconfirmthevalidityofcalculationsinpredictingperformanceandoperatingrange.

Numericalcalculationsallowedtoestimatetheinfluenceofimpellerandvaneddiffusergeometrymodificationsacceptablewithinselectedconstraints.

Thestrategygivespossibilitytodesignhighlyefficientcentrifugalcompressorsoruseexistingcentrifugalcompressorflowpathsinsteadofnewonesthatcanbecreatedby

trimmingtheimpellerwheelattrailingedgevaryingimpellerbladeheightsatleadingandtrailingedgesmodifyingvaneddiffuserheightanditsstaggerangle

Accurateoffdesignflowpredictionsaremadetofindstableoperationrangesofupgradedcentrifugalcompressorflowpaths.

Thedescribedstudyiscarriedoutincollaborationwithlargeturbochargersmanufacturerengagedinlocomotive,marine,heavydutytrucks,drillingrigs,power,andpipelinestationsappliances.

Nomenclature

8/31/2015 CentrifugalCompressorDesignandReratinginTurbochargers

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D1,D2 Impellerinlet/outletdiameter

l1,l2 Impellerinlet/outletbladeheight

Compressorefficiency

Rotationalspeed

C Compressorpressureratio

Figure1.Centrifugalcompressorinturbocharger

Introduction

Centrifugalcompressorsareusedinturbochargersextensivelybecauseoftheirsmoothoperation,theircapabilityforwideoperatingrange,andtheirhighreliability.

Properselectionofthecentrifugalcompressorisanimportantdecisioninfluencingthesuccessfuloperationoftheturbocharger.Thus,completedesignworkflowshouldbeusedtotakeintoaccountallengineeringaspectsinvolvingsequenceofseveralsteps:

Preliminarydesign(sizing)MeanlinecalculationsPerformancemapsanalysisFlowpathoptimizationProfilingand3DbladedesignStructuralandmodalanalysis3Dflowanalysis

Preliminarydesignofcentrifugalcompressorrequiresminimalinputofgeometricalandoperationalconstraintstofindacceptablesizesoftheflowpath.

Meanlinecalculationsandperformancemapsanalysisisthenextsteptorefinethesolution.Somegeometrymodificationscanbemadeduringthissteptooptimizetheefficiencyandmeetrequiredlevelofstableoperatingrange.

3Dbladedesignandprofilingincombinationwithstructural,modaland3Dflowanalysesgivethefinalanswertothequestionwhatkindofflowpathismostsuitableforspecificneeds.

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Centrifugalcompressorreratingisoftenrequiredtomeetnewdesignflowrateorhead.Thesechanges,inmanycases,needthecompressortobe"redesigned".

Itincludesanythingfromasimplespeedchangetotrimmingofimpellers.Inthecaseofvaneddiffuserbeingusedinthecompressor,thecompressorsurgemarginisgreatlyreducedbecauseofchangesinsuctionpressures[1].Thisisduetotheflowangleattheexitoftheimpellerhavingalargeincidenceangleonthediffuserblade.

Inthisarticlesomewaystochangetheheadandflowofexistingcompressorsarediscussedandinvestigated.Compressorreratingrequiresanindepthknowledgeofthecompressoranditscomponents.

Therequirementsforadifferentheadatapproximatelyjustthesameflowwouldrequirechangesinmachinespeedand,insomecases,thetrimmingofthewheels.

Itisalsoknownthattrimmingthecompressorwheelswouldalsoreduceheadproduced.Aspeedincreaseafterthewheelshavebeentrimmedwouldthenincreasetheheaddeliveredatahigherflow[2].

ExperimentalTestFacility

Centrifugalcompressorperformancewasevaluatedusinganexperimentaltestfacility.Centrifugalcompressorwasdrivenbytheaxialturbinestageutilizingthepowerofexhaustgasessuppliedbyconvertedaeroderivativecombustionchamber.Thismethodwasusedbecauseofhighpowerinputlevelthathasbeenneededfordrivingthecentrifugalcompressorinselectedturbocharger.

Thelocationsofpressure,temperature,andflowmeasuringsystemsareschematicallyshownonfig.2.

Inletanddischargepipingwasselectedinthatwaytopreserveflowconditionsthatminimizemeasuringuncertainties.

Dataacquisitionmethodswereusedduringexperimentaldataprocessing.Pressure,temperature,flowmeasuringandrotationalspeedmeasuringinstrumentationwascalibratedbeforecarryingouttheexperimentalstudiestomeetallmeasurementrequirements.

Figure2.Experimentaltestfacility

ProblemFormulation

Currentstudywasintendedtofindquickandreliableapproachtopredictoffdesignperformanceandstableoperatingrangeofnewandupgradedcentrifugalcompressorflowpathsusedinturbochargers.Thestudywasdividedinto

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severalphases:

ValidationofcentrifugalcompressorflowpredictiontoolusingperformancedataobtainedduringexperimentalstudiesofseveralcompressorflowpathsPerformanceandstableoperatingrangepredictionsfordifferentalternativecentrifugalcompressorflowpathmodifications

PreliminaryDesign

Thefirststepofthestudywastocarryoutthepreliminarydesignfromthegroundandfindoptimalsolutionusinggeometricalconstraintsandoperationalboundaryconditionsclosetovaluesofdesignparametersusedincentrifugalcompressor(TK23series)manufacturedbyJSCSKBT.

Preliminarydesignin1Dinverseproblemformulationwasusedtofindthesolutiontakingintoaccountspecifieddesignconditions(=32000rpm,C=3.5).

Arandomsearchmethodisallowedtofindacloudofsolutionpointswithintheselectedranges(fig.3).Themaximumefficiencyistakenascriteriontodefinetheoptimalsolutionpoint.

Figure3.Cloudofsolutionpoints

Figure4.Bestcentrifugalcompressorflowpathselectedafterpreliminarydesign

Resultsfromthepreliminarydesignstudyshowedthatgeometricalandoperationalparametersofanewlydesigned

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flowpathareveryclosetotheoriginalone(fig.4).Thismeansthattheflowpathoftheoriginalcentrifugalcompressorisatitsoptimallevel.

ComparisonofExperimentalandCalculationalResults

Theexperimentalperformancesofseveralcentrifugalcompressorswereevaluatedandcomparedtonumericalcalculations.Comparisonofexperimentalandflowpredictionsforonecasestudyisshownonfig.5.Analysisofperformancemapsshowsgoodagreementofnumericalcalculationswithexperiment.

Figure5.Performancemapscomparisonofexperimentalandcalculationresults

Figure6.Centrifugalcompressor3Dflowpath

Accurateoffdesignflowpredictionsallowedtousethecalculationapproachinfurtherstudiesofupgradedcentrifugalcompressorflowpaths.Numericalstudiestestplanincludesperformanceevaluationoforiginalcompressorflowpathmodificationsdueto

trimmingofimpellertrailingedgediametervaryingimpellerbladeheightsatleadingandtrailingedgesmodifyingvaneddiffuserheightandstaggerangle

EffectofImpellerWheelTrimmingatTrailingEdge

Flowpredictionsweremadeforseveralmodificationstostudytheeffectofimpellerwheeltrimming.Fig.7depictscalculatedperformancemapsforcasestudiesdescribedbellow:

initialflowpathgeometry:impelleroutletdiameterD2=275mm

modification1:wheeltrimming(3.5mm)modification2:wheeltrimming(7mm)

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Figure7.Effectofimpellerwheeltrimmingattrailingedge

EffectofImpellerInletHeightVariation

Flowpredictionsweremadeforseveralmodificationstostudytheeffectofimpellerinletheightvariation.Fig.8depictscalculatedperformancemapsforcasestudiesdescribedbellow:

initialflowpathgeometry:impellerinletheightl1=47.5mm

modification3:impellerinletheightreducing(2.5mm)modification4:impellerinletheightreducing(5mm)

Itisevidentthatchokeinvaneddiffusercausesthecoincidenceofspeedlineswhenperformanceisbeingestimatedonlowerrotationalspeeds.

Figure8.Effectofimpellerinletheightvariation

EffectofImpellerOutletHeightVariation

Flowpredictionsweremadeforseveralmodificationstostudytheeffectofimpelleroutletheightvariationincombinationwithreducingofvaneddiffuserheight.Fig.9depictscalculatedperformancemapsforcasestudiesdescribedbellow:

2=11.4mmmodification5:impelleroutletheightreducing(1mm)modification6:impelleroutletheight

reducing(2mm)

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Figure9.Effectofimpelleroutletheightvariation

EffectofVanedDiffuserStagerAngleVariation

Flowpredictionsweremadeforseveralmodificationstostudytheeffectofvaneddiffuserstaggeranglevariation.Fig.10depictscalculatedperformancemapsforcasestudiesdescribedbellow:

initialflowpathgeometry:defaultvaneddiffuserstaggerangl