Introduction
1.1Introduction
Flightisthedreamofhumanstomoveinaninaccessible,unknownworld.Toachieve thispurpose,humanshavealwaystriedtoinventdevicesandvehicles,whichenable themtomoveinthesky.Duetothehighvelocityofthe fly,theairplanehasbeen widelydevelopedfortransportationforalong-distancejourney.Theadvantagesof flightintheskyhavemotivatedthegovernmenttousethisto fightagainsttheirenemies.Hence,various fightershavebeeninventedthatmoveatahigherspeedthan civilapplications.Then,scientistshavebelievedthattheycouldaccessspacewith high-speedspacecraft,whichmovesintheouteratmosphere.Intheatmospheric domain,thehighestspeedcraftisavailablesinceexistinggasinouterspaceislowdensityandcold.
Therangeofthe fl ightspeedismainlydividedaccordingtotheunitMachnumber knownassonic(M ¼ 1).Whenthe fl ightspeedislessthan M ¼ 1,itisknownassubsonic.Forgreaterspeed fl ight( M > 1),the fl owregimeiscalledsupersonic.When the fl ightspeedissigni fi cantlyhigherthansonic( M >> 1),itisrecognizedashypersonic.Theworldofhigh-speed fl ightisdirectlylinkedwithanentirelyunknown environment,named “hypersonicregime” Thetermhypersonicisintroducedto discriminate fl ow fi eldphenomenaandproblemsthatoccurat fl ightspeeds,and theyaregreaterenoughthanthetypicalsupersonicvelocities.Theadventofnew distinctivefeaturesinhypersonic fl owfeaturejusti fi estheuseofanewterm, differentfromthewell-establishedone supersonic.Hydrodynamicandchemical andphysicalnaturesarethetwomainaspectsofthesehypersonicfeatures.The formerisduetohigh fl ightMach,whilethelatterisrelatedtothehighenergyof the fl ow( Kuchemann,1978 ).Althoughthereareseveralde fi nitionsforthehypersonicaerodynamic, fl owswithMachnumbermorethan5areknownashypersonic regimeaspresentedin Fig.1.1
Indeed,thehypersonicregimeisbestdefinedasthatregimewherecertainphysical flowphenomenabecomeincreasinglymoresignificantandimperativeastheMach numberisincreasedtohighervalues.Forexample,theratioofthermaltohydrodynamicboundarylayerisoneoftheprogressivephenomenafordiscriminationofhypersonicregimefromasupersonicone.Thisratioandothersigni ficantfactorsmay varyaccordingtothegeometryandoperatingconditionofthemodelinthehighspeeddomain.Thisbookhasmainlyfocusedontheseaspectsofhypersonic fl owin detailfortheanalysisofaerodynamicsandaerothermodynamicsofahigh-speed vehicle.
2AerodynamicHeatinginSupersonicandHypersonicFlows
M∞ <0.3
Incompressible subsonic
V<a: M∞ <1
Compressible subsonic: 0.3<M∞ <Mcritical
=0.3
=1
Transonic: Mcritical<M∞ <1.4
V>a: M∞ >1
Supersonic: 1.4<M∞ <5 V>>a: Hypersonic
=5
Figure1.1 Ellipseofmotionregimes.
1.2Structureofthe flow fieldaroundthesuper/ hypersonicvehicles
Toinvestigatethetechniqueforthereductionofaeroheatinganddragforceonthehypersonicforebody,thestructureofthe flow fieldaroundvehiclesshouldbeinitially recognized. Fig.1.2 demonstratestheschematicofa flow fieldaroundatypicalhypersonicvehicle.Ingeneralview,wecandividethe flow fieldaroundthehypersonicvehiclesintothreemainregions:theboundarylayer,inviscid fl owregion,andthewake regionasillustratedin Fig.1.2.
- meyer expansion Outer inviscid
Figure1.2 Typicalhypersonicbody flow fieldincontinuumregime.
In1904,LudwigPrandtlintroducedtheaerodynamicboundarylayerasaregion adjacenttothebodysurface,subjectedtoviscouseffectsandheatconduction.The shearinginfluenceofviscosityresultsinthevelocitygradientoaringfromzeroat thewalltotheouter flowvelocityattheedgeoftheboundarylayer(see Fig.1.3). Inthesubsonicregime,theboundary-layerthickness99%(or)isdefi nedasthenormal distancetothewallwherethelocalvelocityis99%ofthe “free-stream” (orboundarylayeredge)velocityandisrelatedtoRe:
Particularly,asshownin Fig.1.2,thevelocityprofilesintheboundarylayerareunlikerangingfromlaminartoturbulentboundarylayer.Consequently,bothheat flux andshearstressarepresumedtobelargerinthecaseofturbulent flow(Viviani & Pezzella,2015).Thevelocityprofi leintheboundarylayerdeterminestheviscousforces actingonthebody.Thewallshearstress(cg/ms2),isgivenby
Figure1.3 Boundary-layervelocityprofiles.
andthelocalskinfrictioncoef ficient Cf(x)is
Fourier’slawofheatconductionisappliedforthecalculationoftheheattransfer rateonthewall.Thewallheattransferrate(W/m2),andStantonnumberSt,arecalculatedwiththefollowingequations:
where k (W/mK),isthethermalconductivity.
1.3Governingequationsforsupersonic/hypersonic flow
Therecognitionofthemaingoverningequationsforthestudyofeffectivetermsin aerodynamicheatingisessential.Therearethreemainconservationlawsthatgovern all fluid flow:
1. Conservationofmass:continuityequation
2. Conservationofmomentum:Newton’ssecondlawofmotion
3. Conservationofenergy: firstlawofthermodynamics
Byapplyingtheboundaryconditionsofourmodel,solvingtheseequationscould resultinthe flowfeatureandtemperaturedistribution.
Whenitisassumedthatthe flow fieldaroundthemainbodyiscontinuum,theconservationequationsresultinNavier Stokesequationsasasystemofequationsbased onthebulkpropertiesofair.
Incontrast,Boltzmannequation,whichisbasedonmolecularmechanics,isused forarare fied flow fi eld.Tode finethecontinuityofthe fl uid flow,Knnumberiscalculated.WhentheKnnumberishighenough(Kn > 1),thecontinuityassumptionfails, andtheBoltzmannequationmustbeadoptedsince flowismolecular.Regardingthe setofboundaryconditionswithadefinitionofthegas,the flow fi eldpastthebody isobtainedviatheNavier Stokesequations.Actually,airmaybedefinedasaperfect gasforawiderangeofproblems.Consequently,thepressure, p (Pa),calculated p ¼ rRT (1.5) where p isthedensity, T thetemperature,and R thegasconstant.TheNavier Stokes equationsforcompressibleandunsteady floware:
Where T representsthestresstensor, q isthevectorofheat flux,and finally, f and r are theexternalforce fieldperunitmassandtheheatsupplyperunitmassperunittime, respectively.
TheNavier Stokesequationsareasetofcoupled,nonlinear,partialdifferential equations.Theequationsareamixedsetofelliptic parabolicequationsforsteady flowandarehyperbolic parabolicwhentheunsteadytermisrecalled.
WhentheviscousandtheheattransfertermsareignoredfromtheNavier Stokes equations,weattainedasimplifiedsetofequationsknownastheEulerequations: vr
vt þ V:ðruÞ¼ 0 v
AlthoughtheEulerequationsarealsocoupled,nonlinearpartialdifferentialequations, theorderofEulerequationsislowerthantheNavier Stokesequations.TheunsteadyEuler equationsarehyperbolic,butthesteady-stateequationschangetheircharacterfromelliptic insubsonic flow(MN < 1)tohyperbolicinsupersonic flow(MN > 1).
1.4EffectsofMachon flowcharacteristics
Physicalunderstandingofsupersonic fl owishighlyimportanttorecognizethemechanismofaeroheatinganddragreductiondevices.Aperturbanceina fluidgenerates acousticwavesthatpropagatesphericallywiththespeedofsound,a,transmitting theexistenceofthesourcetothe flow field. Fig.1.4 demonstratesthetransmission
Figure1.4 Effectofmovingsourceonwavepropagation. FromViviani,A., & Pezzella,G.(2015).Aerodynamicandaerothermodynamicanalysisof spacemissionvehicles.In Springeraerospacetechnology.SpringerInternationalPublishing. https://doi.org/10.1007/978-3-319-13927-2
6AerodynamicHeatinginSupersonicandHypersonicFlows
Figure1.5 EffectofMachnumber(M)on flowcharacteristicspastanairfoil[2].
FromViviani,A., & Pezzella,G.(2015).Aerodynamicandaerothermodynamicanalysisof spacemissionvehicles.In Springeraerospacetechnology.SpringerInternationalPublishing. https://doi.org/10.1007/978-3-319-13927-2
oftheacousticwavesfromamovingsource(Viviani & Pezzella,2015).Consequently, whenthespeedofthesource, U,islessthansoundvelocity(a),theacousticwaveswill informthenearby fluidoftheupcomingofthesource.Ontheotherhand,theinformationcannottransmitbeyondthesourceandislimitedtoaconeofinfluence,calledthe Machconewhenthesourcemovesfasterthansonicvelocity(a).
Duetovelocityeffectsofsource,theboundaryconditionsarecriticalthroughout thewholeboundaryforsubsonicproblems,andhence,thesearecalled “boundary valueproblems” Conversely,supersonicproblemsareknownas “initialvalueproblems” sinceboundaryconditionsarerequiredonlyatanearlystepwiththesolution gainedbymarchingdownstream.
Accordingtotheaccuracyofsomeoftheassumptionsandthecharacterofthegoverningequations,thecontinuum fl owregimemaybedividedinto fivecategories:
(a) incompressible flow MN < 0.3(constant)
(b) Compressiblesubsonic flow0.3 < MN < 1
(c) Transonic flow0.8 < MN < 1.2
(d) Supersonic flow MN > 1
(e) Hypersonic flow MN > 5
Torecognizethemaindifferencebetweenthese flowtypes, Fig.1.5 demonstratesa prominent flowstructurearoundanairfoilwhenthevelocityofthefreestreamvaries (Viviani & Pezzella,2015).Asshowninthis fi gure,theformationofdifferentshocks andtheiranglesarethemainchangeswhenthefreestreamvelocityincreases.
1.5Aeroheating
Theformationofthestrongbowshockneartheforebodyofsupersonicvehiclesresults inthehigh-temperatureregion.Whenthetemperatureoftheairstreamexceedsa
threshold,theapproximationofperfectgasfortheairstreamisnotvalid.Inextremely highfree-streamMachnumber(M > 30),thetemperaturebehindthestrongshockexceeds10,000K,andthisresultsinthe flowionizationanddissociationthrougha chemicalreaction.Infact,thegasincludesmonatomicanddiatomicparticlesinadditiontoionsandelectronsandthusprogressingina “non-ideal” manner.
Hightemperatureaffectsthevibrationalenergyofthe flowmoleculeandhence,the speci ficheatscpandcvtobecomefunctionsoftemperature.Asthegastemperatureis augmentedfurther,chemicalreactionscanoccurinthisregion.Indeed,cpandcvare functionsofbothtemperatureandpressureforanequilibriumchemicallyreactinggas.
Sincetheairdensityislowatahighaltitude,energyexchangeandchemicalreactionsarenoticeable.Hence,thethermochemicalnonequilibriummodelingisessential fortheanalysisofare-entry flow field.
Torecognizetheeffectsofnonequilibrium flows,assumethatthegasmixturewill involveaconcentrationofatomsandmoleculesofonlyonespecies,N2 orO2 (a diatomicgas).Whenthetemperatureandpressureare800Kand1atm,respectively, thevibrationalenergyofthemoleculesbecomesimportant(Jr.,1989).
Thepropertiesofthegaschangealthoughachemicalreactiondoesnotoccur.When thetemperaturereachesabout2000K,theO2 dissociationsinitiate.Atthe4000K,the O2 dissociationisfundamentallycomplete;mostoftheoxygenisintheformofatomic oxygen,O.Furthermore,N2 initiatestodissociateat4000KandallofN2 dissociated whenthetemperaturereachesat90(X)K. Fig.1.6 summarizesthedissociationprocess indifferenttemperatureranges. Fig.1.7 confi rmsthathigh-temperaturegaseffectsare conventionalinthealtitude velocitymap.
1.6Keyfactorsinthehypersonicregime
Sincethemainobjectofthisbookistoinvestigatetherecenttechniquesforthereductionofdragandaerodynamicheatinginhypersonicvehicles,itisessentialtointroduce themainfeaturesofthehypersonicregime.Hypersonicvehiclesaremainlydivided intothreetypes:missiles,entrybodies,andlaunchvehicles.Aerodynamicheatingoccursduetothetransformationofhighenthalpyandmomentumoftheairstreamto stagnation flowonthetipofthesehigh-speedvehicles.Hence,thereareseveral flowfeaturesthatareconsideredeffectiveonthisphenomenon.Inthefollowing, themainsignificantkeyfeaturesofhypersonic flowassociatedwithaerodynamicheatingareexplained.
1.6.1Bowshock
Duetothehighvelocitiesandangleofincidenceofhypersonicvehicles,strongbow shockwavesaregeneratedaheadofvehicles.Infact, flowdisturbancescannotoperate theirwayupstream,andthedisturbancewavespileupandmergeataspecifi cdistance fromthebody,andastrongwaveisproducedinfrontofthebody(Jr.,1989).
8AerodynamicHeatinginSupersonicandHypersonicFlows
Figure1.6 Assortmentsofdissociation,vibrational,andionizationforairat1atmpressure.
FromViviani,A., & Pezzella,G.(2015).Aerodynamicandaerothermodynamicanalysisof spacemissionvehicles.In Springeraerospacetechnology.SpringerInternationalPublishing. https://doi.org/10.1007/978-3-319-13927-2
Figure1.7 Altitude velocitymapwithcoveredzonesofdissociation,vibrationalexcitation, andionization.
FromViviani,A., & Pezzella,G.(2015).Aerodynamicandaerothermodynamicanalysisof spacemissionvehicles.In Springeraerospacetechnology.SpringerInternationalPublishing. https://doi.org/10.1007/978-3-319-13927-2
1.6.2Aerodynamicheating
Themainchallengeforthedesignofhypersonicvehiclesistheaerodynamicstructure. Althoughslenderstructureseemseffi cientfordragreductionofthesupersonicvehicles,sharpleadingedgewouldresultintheheatingphenomenon. Eq.(1.8) presents therelationbetweenstatictemperatureandstagnationtemperature:
Meanwhile,thetemperatureoftheboundarylayerissubstantiallyhighduetoviscous dissipation(i.e.,frictionbetweenadjacent fluidlayers)producedbytheno-slip boundaryconditionatthewall.Indeed,heatwilltransfertothemainbodybecause ofthehigh-temperature fluidintheboundarylayeruntilthetemperaturegradientatthe walliszero(i.e.,adiabaticwall).
Accordingto Eqs.(1.8)and(1.9),itisfoundthattemperaturecouldincrease severelywhentheMachnumberofthe flightgoesup.Hence,speci ficmaterials, e.g.,titaniumareconsideredtoavoidburningatthetipofhypersonicvehicles.This showsthataerodynamicheatingcausedbyviscouseffectsistheprimaryconcernin thedesignofhypersonicconfigurations.Besides,theReynoldsnumberofhypersonic vehiclesissolow,andthe fl owregimeislaminarsincethey flyathighaltitudes. Indeed,theheattransferismuchlowerwhenthe flowislaminar.Thesephenomena wouldbeexplainedthoroughlyinthenextchapters.
Toavoidexcessiveheatproductioninthenoseofhypersonicvehicles,abluntnose coneisusedalthoughitsdragismorethanaslenderbody.
VanDriestpresentedthatthestagnationregionwiththeheatingrateq0 isproportionaltothesquarerootoftheedgevelocitygradient(due/dx)(Driest,1952).DeJarnetteetal.(1987)presented Eq.(1.10) todisclosetherelationshipbetweenthevelocity gradientandthestagnation-pointradiusasfollows:
Eq.(1.10) indicatesthatstagnation-pointheatingconsiderablyriseswhenthenose ofthebodybecomessharp(R-0).Hence,thebluntlendingedgeisappliedtohypersonicvehicles.Tominimizetheheattransferrate, Eq.(1.10), flatleadingedge(RN) ismorepreferablethroughtheraiseofdragforce,whichreducesthevelocitytoassist asofttouchdown.
10AerodynamicHeatinginSupersonicandHypersonicFlows
1.6.3Surfacepressureeffects
Thepressuredistributiononthebodyofthehypersonicvehicleisasignificantfactor. Intwo-dimensional flow,thepressurecoef ficientcouldbecalculatedby flowing equation:
¼ 2q M 2 1 q
Where q and M aresurfaceslopeandhypersonicMachnumbers,consequently.This estimationisnotsuitableforrealaircraftshapes.However,hypersonicrulesareuseful. TheconceptsofNewtonresultinthemostfamousrelation.AlthoughNewtonwas incorrectforlow-speed flow,hisideadoesapplytohypersonicvelocities.Inthis concept,thehypersonic flowisconsideredasastreamofparticles,whichlosealltheir momentumnormaltoasurfacewhentheyarrived.Thisresultsinthewell-known relation: Cp ¼ 2sin2 q
where q istheanglebetweensurfaceand fl owdirection.Hence,thegeometryofthe bodydeterminesthelocalsurfacepressure.Besides,inthisconcept,theportionofthe bodythatencountersthe fl owisconsideredforparticleseffectsasdepictedin Fig.1.8. Theotherportionofthebodyisrecognizedasshadowwhere Cp ¼ 0.
OneoftheinterestingaspectsofthisformulaistheabsenceofMachnumberinthis equation,theotheroneistherelationofpressurecoeffi cientandthesquareoftheinclinationangleandnotlinearly.Thisconfi rmsthatthehypersonic flowismeaningfully distinctfromthelinearized flowmodelsatlowervelocity.
1.6.4Temperatureeffects
Inhypersonic fl ow,temperatureovercomesathresholdbehindastrongshockwave, andtheaircannotbeconsideredasaperfectgas.Thevariationoftemperaturebehind anormalshockwaveforvariousfree-streamvelocitiesforavehicle flyingatastandard
Figure1.8 Shadowsketchforzonewith Cp ¼ 0. FromViviani,A., & Pezzella,G.(2015).Aerodynamicandaerothermodynamicanalysisof spacemissionvehicles.In Springeraerospacetechnology.SpringerInternationalPublishing. https://doi.org/10.1007/978-3-319-13927-2
Cp
Figure1.9 Temperatureaftera normalshockwaveasafunction offree-streamvelocityata standardaltitudeof52km. FromViviani,A., & Pezzella,G. (2015).Aerodynamicand aerothermodynamicanalysisof spacemissionvehicles.In Springeraerospacetechnology. SpringerInternational Publishing. https://doi.org/10. 1007/978-3-319-13927-2
altitudeof52kmisplottedin Fig.1.9.Inthis fi gure,therearetwocurves:perfectgas andreactinggas.Intheformer,itisassumedthatairstreamactsasperfectnonreacting gaswiththeratioofspecificheat g ¼ 1.4.Inthelatter,theairbehindtheshockis consideredasequilibriumchemicallyreadinggaswhichismorerealistic.Thecomparisonofthesetwolinesindicatesthatairtemperatureinthenoseregionofahypersonic vehiclecouldbeexceedinglyhigh,e.g.,reachingapproximately11,000KataMach numberof36.Besides,thechemicallyreactingeffectsmustbeconsideredforthe calculationofapreciseshocklayertemperature.
1.6.5Viscouseffects
Viscosityisknownasasignificantparameterfortheanalysisofthe flowstructurein thehypersonic flow.Inaconstantpressureprocess,ariseintemperatureresultsina lowerdensity.Consequently,theboundary-layerthicknesswillhavetoincreasetopreservethesamemass flowinthehigher-temperatureboundarylayerlinkedwithsupersonic flows(Jr.,1989).Bythesimilarityapproach,thefollowingequationisachieved fortheestimationofthethicknessoftheboundarylayer.
Bythisequation,itisfoundthattheboundarylayerofthehypersonic flowisthicker thanthatofthesupersonicatacertainReynoldsnumber.Hence,theeffectsofhypersonic flowontheouterinviscid fl ow fi eldpastthevehiclearemoresubstantial.This interactionisknownasviscousinteraction.
d x f M 2 N Rex p (1.13)
1.6.6Entropygradient
Fig.1.10 demonstratesdifferentlayersaroundthebluntnoseatthehypersonicMach number.Athinshocklayerisproducedoverthebluntnosewithasmallshockdetachmentdistance, d.Theentropyofthe fl owrisesacrossashockwave,andthis expandsmorewhentheshockbecomeslarger.
Asdepictedinthe figure,the “entropylayer” extendsdownstreamalongthebody forlargedistancesfromthenose.Inthislayer,theentropygradientishigh,andthe boundarylayeriswithinthislayerandthisentropygradientaffectsthehydrodynamic boundarylayer.
Toperformastandardboundary-layercalculationonthesurface,theentropylayer isproblematic.Indeed,theproperconditionsattheouteredgeoftheboundarylayer areunknown.
1.6.7Shocklayer
Theshocklayerisknownasthe flowregionbetweenthebodyandtheshockwave.In thehypersonicregion,thislayerisverythin,asdemonstratedin Fig.1.11,i.e.,the angleoftheshocklayerisabout18degreesforawedgeof15semi-anglesina fl owat M ¼ 36whenstandardobliqueshocktheoryisappliedandtheairstreamis consideredaperfectgas.Byconsideringrealgasconditions,theseanglesalso decrease.Inhypersonic flow,theshocklayeristhinandhighlyclosetothemain body.In1687,IssacNewtonproposedathinshocklayertheoryformodelinghypersonic flow.Thismodelwaspresentedfortheestimationofthepressuredistribution overthesurfaceofahypersonicbody.
Figure1.10 Theentropylayer. FromViviani,A., & Pezzella,G.(2015).Aerodynamicandaerothermodynamicanalysisof spacemissionvehicles.In Springeraerospacetechnology.SpringerInternationalPublishing. https://doi.org/10.1007/978-3-319-13927-2 12AerodynamicHeatinginSupersonicandHypersonicFlows
Figure1.11 Thinhypersonicshocklayer.
FromViviani,A., & Pezzella,G.(2015).Aerodynamicandaerothermodynamicanalysisof spacemissionvehicles.In Springeraerospacetechnology.SpringerInternationalPublishing. https://doi.org/10.1007/978-3-319-13927-2
1.7Nondimensionalnumbers
Sincethe fl owfeaturearoundtheforebodyofhypersonicvehiclesiscomplicated, severalphysicalphenomenabecomecriticalforthesurvivabilityofthespacecraft. Hence,comparisonofthesephenomenaissignificant,andthisconfirmstheimportance ofdimensionalanalysis.Inthefollowing,importantdimensionlessratiosarelisted:
Machnumber M ðÞ¼ macroscopicspeedfluid speedofsoundinthefluid ¼ V =a
Reynoldsnumber ðReÞ¼ Inertialforce Viscousforce ¼ mv sA ¼ rAV 2 m V Lref A ¼ rVLref m ¼ Re
Prandtlnumber ðPr Þ¼ Viscousdissipationenergy Energyconducted ¼ sAV _
Lewisnumber ðLeÞ¼ thermaldiffusivity massdiffusivity ¼ a D
Stantonnumber ðStÞ¼ heattransfercoefficient heatcapacity ¼ h ruCp
1.8Differenttechniquesforthethermalprotectionand dragreductionofspacevehicles
Therearethreetypesofhypersonicvehicles:wingedreentryvehicles,unwinged reentryvehicles,andcruiseandaccelerationvehicles(Weiland & Hirschel,2015). Spaceshuttlesandinterplanetaryvehiclesarerecognizedastypicalwingedre-entry
14AerodynamicHeatinginSupersonicandHypersonicFlows
vehicles,whilecommercialreusablemissilesandballisticmissilesareunwinged re-entryhypersonicvehicles.Hypersoniccruisemissilesandhypersonicplanesare classifiedascruiseandacceleratingvehicles. Fig.1.12 demonstratesexamplesofthese categories.Theformertwohavebeencharacterizedbybluntforebodyconfi gurations. Indeed,themaindesignalternativeisbluntingtheforebodyofthesehypersonicvehicles(Bogdonoff & Vas,1959).Whentheforebodyofhypersonicvehiclesisblunted, thepeak(stagnation)aeroheating fluxlevelsdecline(Menezesetal.,2002),andoperationandaccommodationofcrewareimproved,andconsequently,volumetricefficiencyisincreased(Gauer & Paull,2008; Shoemaker,1990).Infact,existing launchfacilitiesbecomecost-effectiveforlongermissilesbythismethod(PeterRedingetal.,1977).Themaindisadvantagesofbluntforebodiesareextremelyhighdrag forceandaero-thermodynamicimpacts.
Themainobjectinthedesignoftheforebodiesistoreduceaeroheatinganddragforce simultaneously.Whenthedragforceofvehiclesisdecreased,therangeofcrewincreases, andthepropulsionsystemcanbelowandpayloadcapacityishigh,andfuelconsumption ismoreefficient.Asaeroheatingislimited,forebodystructure(Huebneretal.,1995)and on-boardequipment(Shoemaker,1990)areprotectedeffectively,whilealowthermal protectionsystem(TPS)isrequired.Astrongbowshockwaveaheadoftheforebody isthemainsourceofhighaeroheatinganddragforce,impactingtheforebodiesinsupersonic/hypersonic flightregime.Theformationofhighdragandaeroheatingontheforebodyismainlyduetoextremetemperatureandpressuregradientdownstreamof foreshock.Therefore,reformingthe flow fieldaheadoftheforebodytoweakenthe bowshockcoulddecreasebothaeroheatinganddrag,simultaneously.
Figure1.12 Typicalhypersonicvehiclesofdiversetypes. FromAhmed,M.Y.M., & Qin,N.(2020).Forebodyshockcontroldevicesfordragandaeroheatingreduction:Acomprehensivesurveywithapracticalperspective. ProgressinAerospace Sciences,112,100585. https://doi.org/10.1016/j.paerosci.2019.100585
Theprimarygoalofthisbookistopresentandevaluateconceptsofvariousshock controltechniquesforthereductionofaeroheatinganddraginthesupersonicforebody.Thisstudyfocusesontechniquesthatresultinhighdragandaeroheating,i.e., bowforeshock,ratherthanthoseactingtolightentheconsequencesoftheseorigins. Thisbookwouldstudytechniquesthatreformthe flowstructureaheadoftheforebody throughsubstitutingastrongbowforeshockwaveaheadwithamuchweakershock systemorremovingitfromthehypersonicvehicleforebody.Accordingtotheconcept bywhichthe fl ow fieldstructureismodi fied,therearethreemaintypesofthesedevices: fluidic,mechanical(structural),andthermal(energetic)devices.In fluidicdevices, fluidjetsareinjectedintotheincomingfreestream.Ontheotherhand,the applicationofaphysicalbodythatprotrudesaheadoftheforebodyintotheincoming freestreamisknownasastructuraldevice.Inenergeticdevices,anenergyspotis appliedtothefreestreamaheadoftheforebody.Besides,thecombinationofthese basicmethodsisalsousedasahybridtechniqueforthemanagementofdragandaeroheatinginthesupersonic flow field. Fig.1.13 demonstratesthesetypesofforebody shockcontroldevices(Ahmed & Qin,2020).
Themaingoalsofthisbookareto:
• Classifythediversestrategiesinaphysics-basedsystematicway
• Conductareasonableexaminationoftheprimaryphysicalprinciplesandmechanismsof operationforeachdevice
• provideaninclusiveandcriticalreviewofpreviousworksinthe fieldandestablishthecurrentknowledge,
• explainareasofdebateandknowledgegapsforforthcominginvestigationsratherthanreconsideringpreviouslyconventionalknowledge,
• disclosethesubjectsofpracticalimplementationanddesigntradeoffsassociatedwitheachof thesedevicesinrealsystems,
• listtheaccessiblecurrenthypersonicvehiclesthathavealreadyappliedthesedevices.
Figure1.13 Physics-basedarrangementofaeroheatinganddragreductiontechniques. FromAhmed,M.Y.M., & Qin,N.(2020).Forebodyshockcontroldevicesfordragandaeroheatingreduction:Acomprehensivesurveywithapracticalperspective. ProgressinAerospace Sciences,112,100585. https://doi.org/10.1016/j.paerosci.2019.100585
16AerodynamicHeatinginSupersonicandHypersonicFlows
References
Ahmed,M.Y.M.,&Qin,N.(2020).Forebodyshockcontroldevicesfordragandaero-heating reduction:Acomprehensivesurveywithapracticalperspective. ProgressinAerospace Sciences,112,100585. https://doi.org/10.1016/j.paerosci.2019.100585
Bogdonoff,S.M.,&Vas,I.E.(1959).Preliminaryinvestigationsofspikedbodiesathypersonic speeds. JournaloftheAerospaceSciences,26(2),65 74. https://doi.org/10.2514/8.7945
DeJarnette,F.R.,Hamilton,H.H.,Weilmuenster,K.J.,&Cheatwood,F.M.(1987).Areview ofsomeapproximatemethodsusedinaerodynamicheatinganalyses. JournalofThermophysicsandHeatTransfer,1(1),5 12. https://doi.org/10.2514/3.1 Driest.(1952). Investigationoflaminarboundarylayerincompressible fluidsusingtheCrocco method,NACA-TN-2597.NACAReport. Gauer,M.,&Paull,A.(2008).Numericalinvestigationofaspikedbluntnoseconeathypersonicspeeds. JournalofSpacecraftandRockets,45(3),459 471. https://doi.org/10.2514/ 1.30590
Huebner,L.D.,Mitchell,A.M.,&Boudreaux,E.J.(1995).Experimentalresultsonthe feasibilityofanaerospikeforhypersonicmissiles.In 33rdAerospacesciencesmeetingand exhibit.AmericanInstituteofAeronauticsandAstronauticsInc,AIAA. https://doi.org/ 10.2514/6.1995-737
Jr.(1989). Hypersonichightemperaturegasdynamics.McGraw-HillBookCompany. Kuchemann.(1978). Theaerodynamicdesignofaircraft Menezes,V.,Saravanan,S.,&Reddy,K.P.J.(2002).Shocktunnelstudyofspikedaerodynamicbodies flyingathypersonicMachnumbers. ShockWaves,12(3),197 204. https:// doi.org/10.1007/s00193-002-0160-3
PeterReding,J.,Guenther,R.A.,&Richter,B.J.(1977).Unsteadyaerodynamicconsiderations inthedesignofadrag-reductionspike. JournalofSpacecraftandRockets,14(1),54 60. https://doi.org/10.2514/3.57160
Shoemaker,J.M.(1990).Aerodynamicspike flowfieldscomputedtoselectoptimumconfigurationatMach2.5withexperimentalvalidation.In 28thAerospacesciencesmeeting, 1990.AmericanInstituteofAeronauticsandAstronauticsInc,AIAA. https://doi.org/ 10.2514/6.1990-414
Viviani,A.,&Pezzella,G.(2015). Aerodynamicandaerothermodynamicanalysisofspace missionvehicles.SpringerAerospaceTechnology.SpringerInternationalPublishing. https://doi.org/10.1007/978-3-319-13927-2
Weiland,C.,&Hirschel,E.(2015). Selectedaerothermodynamicdesignproblemsofhypersonic flightvehicles.AlAA,9783540899747.
