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