a topological study of a rankine cycle turbofan engine for use in a super circulation wing...

7/31/2019 A TOPOLOGICAL STUDY OF A RANKINE CYCLE TURBOFAN ENGINE FOR USE IN A SUPER CIRCULATION WING CONFI

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ATOPOLOGICALSTUDYOFARANKINECYCLETURBOFANENGINEFORUSEINASUPERCIRCULATIONWINGCONFIGURATIONFORTRANSPORTAIRCRAFT

ValeriuDRGAN1

1Correspondingauthor

POLITEHNICAUniversityBucharest,FacultyofAerospaceEngineering

Str.GheorghePolizu,nr.1,sector1,011061,Bucharest,Romania

[email protected]

Keywords:Rankinecycle,turbofanengine,supercirculation,CoandeffectAbstract.Thepaperdescribesanefforttointegrateahighpowerhighefficiencypropulsionsystemwithinanaircraftstructure.Rankine cycleshavebeenusedasanalternative toBrayton cycles fora long time in theenergy industrydue to theirhigher

efficiency and low temperature gradient requirements.Using a Rankine cycle topower an aircraft canprovequiteuseful in

reducingfuelconsumptionandincreasingtheBreguetrangeofanaircraftwhilealsominimizingthepollutantemissions.

So far, conventionalaircraft configurations couldnot copewith the largeheatexchangers requiredby the close circuitsofa

Rankinecycle.However,analternativeconfigurationexists:thesupercirculationwing,whichofferstheperspectiveofintegrating

alargecoolingcircuitonthesupercirculatedsideofthewing,thusprovidingaviableoverallconfiguration.

Inasupercirculationconfiguration,airfromthefanoftheengineispassedoveralargeportionofthewing,beingdivertedvia

theCoandeffectandgeneratingadditionalliftboththroughdecreasingthestaticpressureoversaidportionofthewingandbythemomentumof thediverted fluidmass.Thesupercirculatedareacanbemadeuseofby integrationofanadditionalheat

exchangerforcoolingtheworkfluidslightlysuperheatedmercuryvapors.

Acasestudyispresentedwithbothschematicsandpreliminarycalculationsthatjustifythesupercirculationconfigurationforthe

Rankinecycleturbofanaeroengine

Introduction. Historically, thenuclearaeronauticalpropulsionattempts reliedon twobasic ideas:open circuitandclosed circuitheatingof thecore flowasan

alternativetoacombustionchamber,Ref[1],[2], [3].Boththesearchitectureswerebasedonderivativesofconventionalturbojetenginesandreliedonhigh

powernuclearmaterialswhicharegammaradioactive toheattheairflowingthroughtheengine.Anotherimportantaspectofthistypeofpropulsionunitsis

that theymustwork by the Brayton cyclewhich, is inmany aspects inferior to the Rankine cycle used by sea going types of nuclear turbine propulsors.

Fundamentallytheproblemhasalwaysbeenthecapacitytocooltheworkingfluidafterexitingthelastturbinestage.

Thesupercirculationwing(SCW)aircraftofferstheprospectofinstallingcoolingcircuitsdirectlyinthedownwashofthefanflow.Sincethefanflowis

unheated,itwillbeabletoactasacoolingagentfortheworkingfluid.Anotheradvantagewouldbethetipicalrelativelowwingloadingsofthisconfiguration.A

comparisonbetweenanAntonovAn74andanAirbusA320canbeseen intable1.TheSCWhasbeentraditionallyusedforSTOLaircraftRef[4].However,it

couldbeconvertedtonormaltakeoffandlandingbutwithhigherpayloadcapacity.

Sincethedesiredapplicationisdestinedtocivilianpassengertransport,theuseofgammaemmitingnuclearmaterialsisunacceptable,thereforewe

mustseekanalternatehighpowerdensitynuclearmaterialthatdoesnotemitharmfulradiationsandrequirelittleornoshielding.Onesuchmaterialcouldbe

Polonium210, abetaemitting isotopewhichhas apowerdensityof 140 kW/kgRef[5]. The toxicity levelofPo210 is still veryhighhowever it isgenerally

associatedtoingestionhazardsortoexposureofopenedwounds,inwhichcasethebetaparticleswouldenterthebloodstreamdirectlly.

Becauseofthelimitedvolumetriccapacityofferedbyanairliner,theworkingfluidwillhavetobeasdenseaspossible.References[6]and[7]describe

mercuryvaporturbinepowerunits.Thethermalconductivityofmercuryismuchhigherincomparisontootherworkingfluidsencounteredinthepowerplant

industry, thereforetheheatexchangerswillhavehigherheattransfer ratiospersquaremeterRef[8]. It isalso importanttonote thatsomestateof theart

waterammoniapowerplantsmanagesimilarperformancesexceptfortheheattransfer ofthatofthemercuryvaporunits,Ref[9].Thetoxicityofmercuryis

quitehigh, therefore stepsmustbe taken inorder to insure thatno leaksoccuratany stageof the thermomechanicalprocess.Caremustbe takenwhen

designing theairframeandheatexchangersdue to the fact thatmercury chemicallycorrodesaluminumalloysbycatalyzing itsoxidation,Ref [10].The low

temperatureheatexchangerscouldbemadeoftitaniumwhichisoneofthefewmetalsthatdonotformamalgams.

Table 1

parameter Airbus A320 Antonov An-74

Wing loading [kg/m2] 778.96 350

Thrust to weight 0.55 0.829

Wingspan [m] 34 31

MTOW [t] 68 34.5

Minimum air speed [m/sec] 53 30

Thecase

sudy.

ThecurrentcasestudyislookingintothefeasibilityofdesigningaSCWaircraftwithPo140nuclearpowerbymeansofaclosedcircuitmercuryvapor

Rankinecycle.


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Forestimation,thestudyisbasedonanAirbusA320withCFM565aturbineengines,withthesoledifferencebeingtheconfigurationofthewingand

nacelle.

BasedontheavailabledataRef[11],thetotalpowergeneratedbythetwoturbofanenginesoftheaircraft incruise isestimatedatacombined12

MW.Becausethispowerisgeneratedtroughathermodynamiccycle,thecycleefficiencywillbetakenintoaccountbyEq.(1).

Thereforetheminimumtotalmass[kg],ofnuclearmaterialwillbe:

/, (1)

m=143 kg

The available cooling aria of the system per engine, estimated for the preliminary geometry is:

(2)

A~40m2

Considering a heat exchange rate od 200 WK/m2, we obtain the temperature gradient:

350 K

OneparticularaspectoftheRankinecycleisthatundercertainconditions,i.e.ifthecycletakesplacebeneaththevaporizationcurve,itbehaveslikea

Carnotcycle. Inour case, thermodynamicefficiencywillbeconsideredmore important than increasing themechanicalworkandhencewewillconsider theCarnotefficiency:

1

~0.6 (3)

Inothercases,wherethemechanicalworkismoreimportant,theRankinecycleefficiencywillbecalculatedbythemasicenthalpyoftheworkingfluid.

Designingandoptimizingofthecyclemustkeepinmindthevaporizationcurveofeachworkingfluid.

Thetopologyofthestudiedconfiguration:

Fig.1 The flowchart of the desired work fluid circuit within the propulsion unit

Reheatingisusedateverystatorguidevaneinordertopreventhighlyerosivedropletformation,thisisusedasaformofmultiplesmallsuperheating

processesthatmaintainthehighefficiencyofthecyclewhileprovidingmaximummechanicalworkinthegivensituation.

Table 2: Mass comparison of the two propulsion concepts

Component Nuclear Rankine Turbofan Fossil Fuel Brayton

Fuel mass for max Brreguet Range [kg] ~143 19500

Compressor Condenser + Pump Compressor

Turbine 5 stages austenitic steel 7 stages l superalloy

Heater+preheater (combustor) Integrated regenerator + 1 spiraled

superheater-accounted for in fuel mass

1double annular burner

Cooler circuit [kg] Nacelle and FGV + wing passive and active

integrated~70

- No intercooler-Working fluid mass [kg] ~130 Working fluid is ambient air [130

kg/sec]

total ~350 kg 19500 kg

Pump condenserFanVane

cooler

Nacelle

cooler

Passivewing

cooler

Activewing

cooler

Turbineexit

collector

Engine

Superheater

LP

Turbine

Interstage

superheater

HP

Turbine

Recuperator


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Table 3: Air safety advantages and challenges of the Rankine nuclear propulsion

Fig.1 The flow of mercury vapor inside the engine

1.Mercury Vapor Turbine2.Fan

3.Fan stator with integrated cooler

4.Fan Duct with spiral cooler

5.Regenerator

6.Primary spiral superheater

7.Turbine vane integrated

superheater

8.Supercirculated Wing

active cooler

9.Supercirculated Wing

passive cooler

10.Coand flap

11.collecting chamber

12.Condenser13. Liquid mercury pump

Fig.2 Full schematics of the Rankine Nuclear Turbofan integrated

in a SCW airframe

Conclusions. 1.Intermsofnuclearpoweredpropulsion it ismuchmore economically and technically feasible to use turbofansinsteadofusingairheatingturbojets.

2.Rankinecycles

offer

great

perspective

in

terms

of

thermal efficiency and in lowering the manufacturing andmaintenancetechnologycosts` 3.In terms of working fluids, mercury vapors offergreatercompactnessdue tothehigherheattransfercapabilityand also the higher density which decreases the storagevolume.

4.Aluminium alloys should be replaced fromstructural components with eyther other metals or withcompositematerials,withspecialattentiongiventotheeffectsofheatemanatedbythepoloniumsource

5.The alpha nuclear power source is a viablealternative to conventional fuel foruse inairlinersdue to thelow toxicity levels and thehighpoweroutputs, although costandaccessibilityofthematerialarestillveryimportantissues.

advantages conceirns

Very high thermodynamic efficiency Polonium 210 is expensive

Unlimited range / loiter time Nuclear materials need special storage/handling

Less prone to fire in event of crash Very toxic to the environment if crashed

Lower minimum air speed Mercury vapors are toxic to humans if inhaled

Lower Chemical pollution levels

Lower noise

Shorter take off runs

ai

R


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6.Thehighliftprovidedbythesupercirculationwingconfigurationalsoofferstheperspectiveofmoreamplecoolingcircuitswhich,inturnincreases

theefficiencyoftheRankinecycleused

7.Nuclearturbofantechnologiescouldopentheperspectiveof largesupersonicairliners ifsufficientreheatingcouldbeobtainedbybethanuclear

means.

Acknoledgements.ToProf.Dr.Ing.VirgilStanciuformentoringandguidance

TheworkhasbeenfundedbytheSectoralOperationalProgrammeHumanResourcesDevelopment20072013oftheRomanianMinistryofLabour,Familyand

SocialProtectionthroughtheFinancialAgreementsPOSDRU/88/1.5/S/60203.

References[1]RaulColonFlyingonNuclear,TheAmericanEfforttoBuiltaNuclearPoweredBomber

[2]JimWinchesterConceptAircraft:Prototypes,XPlanes,andExperimentalAircraft;(ThunderBayPress2005,ISBN13:9781592234806)

[3]AircraftNuclearPropulsionProgram;(MetalProgress1959ISBN13:9781154622966)

[4]DeLaMontanya,J.B.,Marshall,D.D.,CirculationControlandItsApplicationtoExtremeShortTakeOffandLandingVehicles,(AIAA20071404,January2007)

[5]Polonium(ArgonneNationalLaboratory,EVSHumanHealthFactSheet,August2005)

[6] LuzlrenceW. Gertsma and DavidW.Medwid DESIGN AND FABRICATION OF A COUNTERFLOW DOUBLECONTAINMENT TANTALUM STAINLESSSTEEL

MERCURYBOILER(LewisResearchCenterCleveland,OhioNASA TN D5092)

[7]Jones,LloydMercuryvaporturbine(UnitedStatesPatent1804694T.05/12/1931)

[8]Hammond,C.R(TheElements,inHandbookofChemistryandPhysics81stedition.CRCpress.ISBN08493048142000)..

[9]http://www.aqpl43.dsl.pipex.com/MUSEUM/POWER/mercury/mercury.htm

[10]Vargel,C.;Jacques,M.;Schmidt,M.P.(CorrosionofAluminium.Elsevier.p.158.ISBN20049780080444956.2004).

[11]www.cfm56.com/

a topological study of a rankine cycle turbofan engine for use in a super circulation wing...

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