Aerothermodynamic Optimization of Hypersonic Vehicle TPS Design ...
Aerothermodynamic Analysis of Space- Vehicle Phenomena - ESA
11
Aerothermodynamic Analysis of Space- Vehicle Phenomena J. Muylaert, W. Kordulla, D. Giordano, L. Marraffa, R. Schwane ESA Directorate of Technical and Operational Support, ESTEC, Noordwijk, The Netherlands M. Spel, L. Walpot, H. Wong ATOS BV, Leiden, The Netherlands Introduction By adding thermodynamics to aerodynamics, one arrives at the notion of ‘aerothermo- dynamics’, in which those flow fields are considered, the analysis of which requires - beyond its use in classical aerodynamics - the consideration of special thermodynamic relations. Well-known examples are the high- temperature flows past re-entry vehicles, and flows in combustion chambers and in the nozzles of propulsion systems. The design of space vehicles depends crucially upon databases providing the forces, moments, temperatures and heat fluxes along the chosen trajectories. These databases can be established for given shape and control surfaces, for an assumed centre of gravity, where the shape and control surfaces of the space vehicle need to be determined in an iterative manner until stable and controllable flight is achieved. If the thermal-protection system chosen does not tolerate the loads encountered along the trajectory, the latter has to be adapted such that the flight remains controllable, by changing the space vehicle’s shape and/or its control surfaces. In such multidisciplinary iterations, the available data- bases play a key role. The problem becomes more complex if the aeroelastic effects are considered and integration of the propulsion system is required, the latter being most important for future launchers. Figure 1 indicates the strong interaction between aerothermo- dynamics and other disciplines. Aerothermodynamic tools for design purposes Aerothermodynamic design issues can be addressed using advanced analysis methods, ground-based facilities, and flight testing. In a classical approach, the design of space vehicles (e.g. the Space Shuttle) depends heavily on experimental data. Owing to the inherent limitations of similarity laws, ground- based facilities cannot simulate fully the physical flows around space vehicles during reentry. In the USA, therefore, data obtained from in-flight experiments, particularly with the X-vehicles, have been used to complement the test data obtained from ground-based facilities. The latter contribute to the data required for design work up to Mach 10. These so-called ‘cold’ wind-tunnel data provide the ‘anchor’ points for the extrapolation to flight conditions. In the Hermes era, Europe chose to complement the knowledge available from the cold wind tunnels, which are not able to model Aerothermodynamics is a key technology for the design and optimisation of space vehicles because it provides the necessary databases for, for example, the choice of trajectory, for guidance, navigation and control, as well as for the thermal-protection and propulsion systems. Computational aerothermodynamics, in particular, has become a powerful tool for improving our understanding of the physical phenomena that are at work. This article presents its current capabilities with respect to flow phenomena. Examples are presented of external flows past re-entry- vehicle demonstrators and launchers. Internal flow problems associated with propulsion and the interactions with external flow are also presented. The future work requirements for further strengthening the computational and testing capabilities in Europe are identified. These objectives would be facilitated by bringing together a European network of industry, research organisations and universities. The need to verify ground-based tests with in-flight experiments, i.e. vehicle demonstrators, is also addressed. aerothermodynamic analysis The development of aerothermodynamics in Europe experienced a substantial boost in the mid-eighties within the framework of ESA’s development efforts for the Manned Space- flight Programmes, such as Hermes, and later in the framework of the follow-up Technology Programmes. This was especially true of the development of the hypersonic high-enthalpy facilities, as well as for computational aero- thermodynamics. Since then, aerothermo- dynamics has evolved to cover a wide field of applications and its use is becoming increasingly multidisciplinary. 69
Transcript of Aerothermodynamic Analysis of Space- Vehicle Phenomena - ESA
Aerothermodynamic Analysis of Space-Vehicle Phenomena
J. Muylaert, W. Kordulla, D. Giordano, L. Marraffa, R. SchwaneESA Directorate of Technical and Operational Support, ESTEC, Noordwijk, The Netherlands
M. Spel, L. Walpot, H. WongATOS BV, Leiden, The Netherlands
Introduction By adding thermodynamics to aerodynamics,one arrives at the notion of ‘aerothermo-dynamics’, in which those flow fields areconsidered, the analysis of which requires -beyond its use in classical aerodynamics - theconsideration of special thermodynamicrelations. Well-known examples are the high-temperature flows past re-entry vehicles, andflows in combustion chambers and in thenozzles of propulsion systems.
The design of space vehicles depends cruciallyupon databases providing the forces,moments, temperatures and heat fluxes alongthe chosen trajectories. These databases canbe established for given shape and controlsurfaces, for an assumed centre of gravity,where the shape and control surfaces of thespace vehicle need to be determined in aniterative manner until stable and controllableflight is achieved. If the thermal-protectionsystem chosen does not tolerate the loadsencountered along the trajectory, the latter hasto be adapted such that the flight remainscontrollable, by changing the space vehicle’s shape and/or its control surfaces. In suchmultidisciplinary iterations, the available data-bases play a key role. The problem becomesmore complex if the aeroelastic effects areconsidered and integration of the propulsionsystem is required, the latter being mostimportant for future launchers. Figure 1 indicatesthe strong interaction between aerothermo-dynamics and other disciplines.
Aerothermodynamic tools for designpurposesAerothermodynamic design issues can beaddressed using advanced analysis methods,ground-based facilities, and flight testing. In aclassical approach, the design of spacevehicles (e.g. the Space Shuttle) dependsheavily on experimental data. Owing to theinherent limitations of similarity laws, ground-based facilities cannot simulate fully thephysical flows around space vehicles duringreentry. In the USA, therefore, data obtainedfrom in-flight experiments, particularly with theX-vehicles, have been used to complement thetest data obtained from ground-based facilities.The latter contribute to the data required fordesign work up to Mach 10. These so-called‘cold’ wind-tunnel data provide the ‘anchor’points for the extrapolation to flight conditions.In the Hermes era, Europe chose tocomplement the knowledge available from thecold wind tunnels, which are not able to model
Aerothermodynamics is a key technology for the design andoptimisation of space vehicles because it provides the necessarydatabases for, for example, the choice of trajectory, for guidance,navigation and control, as well as for the thermal-protection andpropulsion systems. Computational aerothermodynamics, inparticular, has become a powerful tool for improving ourunderstanding of the physical phenomena that are at work. Thisarticle presents its current capabilities with respect to flowphenomena. Examples are presented of external flows past re-entry-vehicle demonstrators and launchers. Internal flow problemsassociated with propulsion and the interactions with external flow arealso presented.
The future work requirements for further strengthening thecomputational and testing capabilities in Europe are identified. Theseobjectives would be facilitated by bringing together a Europeannetwork of industry, research organisations and universities. The needto verify ground-based tests with in-flight experiments, i.e. vehicledemonstrators, is also addressed.
aerothermodynamic analysis
The development of aerothermodynamics inEurope experienced a substantial boost in themid-eighties within the framework of ESA’sdevelopment efforts for the Manned Space-flight Programmes, such as Hermes, and laterin the framework of the follow-up TechnologyProgrammes. This was especially true of thedevelopment of the hypersonic high-enthalpyfacilities, as well as for computational aero-thermodynamics. Since then, aerothermo-dynamics has evolved to cover a wide field ofapplications and its use is becoming increasinglymultidisciplinary.
69
MUYLAERT 2/20/01 2:34 PM Page 1
Figure 1. Interactionsbetween
aerothermodynamics andother disciplines
the high-temperature effects typical for higherspeeds and altitudes, by means of high-enthalpy or hot-flow facilities. ESA hassupported the modernisation of existing coldwind tunnels, and also the construction offacilities with new capabilities.
Facilities that were initiated during the HermesProgramme and completed or upgraded duringthe follow-up Manned Spaceflight andTechnology Programmes include: – Two high-enthalpy facilities, which are
mutually complementary, for the study ofhigh-temperature effects on controllabilityand heating: the ‘hot shot’ facility F4 atONERA Le Fauga, and the piston-driven‘shock tube’ HEG at DLR Goettingen.
– Three plasma facilities, also mutuallycomplementary, to investigate the heat loadand gas surface interaction on materials andstructures: the segmented arc-jet-heated L3Kfacility at DLR Cologne (max. power 6 MW),more recently the larger Scirocco facility atCIRA Capua (max. power 70 MW), as well asthe recently commissioned plasmatron facilityat VKI Brussels (max. power 1.2 MW).
The Scirocco facility is still in the commissioningphase, but should be operational in 2001; theother facilities are already in full operation.
In 1997, Europe decided to carry out full-scalefree-flight experiments and embarked on theAtmospheric Re-entry Demonstrator (ARD)capsule. The corresponding post-flight analysishas recently been completed. A lifting-body re-entry demonstrator (X-38) will be flown in 2002based on a close partnership with NASA,where ESA’s and the German TETRAprogramme have joined forces. In February2000, a low-cost flight experiment based onInflatable Re-entry and Descent Technology
(IRDT) from Russia, initially foreseen for a Marslander, was carried out. This flight experiment isbeing repeated in 2001 to evaluate its potentialas an independent, low-cost Space-Stationpayload return vehicle in greater detail. Inaddition to ground-based facilities and the littleavailable flight testing so far, the tool that hasbeen developed most since the Hermes era isComputational Fluid Dynamics (CFD). CFD isbeing used to gain greater insight into thephysical phenomena and to help to accelerateand improve the design processes.
CFD has become a powerful tool in classicalaerodynamics, but its usefulness relies on inputfrom appropriate physical modelling, forexample transition and turbulence for thenumerical integration of the flow governingReynolds averaged Navier-Stokes equations.Hence, measurements in ground-basedfacilities provide the skeleton or anchor pointsfor the database below Mach 10. Thecorresponding ‘interpolation’ is performed withthe results of validated CFD solvers. AboveMach 10, where in particular high-temperatureeffects dominate the flow, CFD must be used.The appropriate validation of CFD is thereforeof great concern. It is achieved by comparingdata measured in, for example, the above-mentioned high-temperature facilities withthose obtained by numerical prediction. Inmany cases the use of CFD goes hand in handwith the definition of the test cases andinterpretation of the data. In this context,ESA/ESTEC and others have organised anumber of workshops in the past. CFD issubsequently being used for flight simulationsabove Mach 10. This ‘extrapolation method’assumes, however, that the physical modelsthat enable good results for the simulation ofthe experimental test case, will provide goodresults also for free flight. Therefore, free-flight
r bulletin 105 — february 2001
70
MULTI DISCIPLINARY INTERACTION
AEROTHERMODYNAMICS
PROPULSION SYSTEMINTEGRATIONPLUME INTERACTIONS
AEROELASTICITYPHYSICAL MODELLINGSURFACE PROPERTIES
ROUGHNESS/TRANSITIONCATALICITYEMISSIVITY
TPS,HEAT LOADS
BODY SHAPE,FLIGHT TRAJECTORY,
GNC
MUYLAERT 2/20/01 2:34 PM Page 2
Figure 2. ARD Schlierenphotograph taken in theONERA S4 facility at Mach10 (incidence angle 20 deg)and the correspondingcomputed iso Mach lines
The ARD flight was a major achievement forEurope. It provided real flight data and enabledcomparison with experimental and numericaldesign tools used for all flight phases. Datawere recorded from the de-orbiting, throughoutthe high-speed portion of the flight, untilparachute deployment and splashdown.Reaction and control system efficiencies, localheating, blackout, transition phenomena anddynamic and static stability data were allmeasured. The splashdown in the Pacificoccurred less than 5 km from the expectedposition. The ARD’s angle of attack and flight-path angle differed only slightly from theprediction (around 2 deg for trim and 0.5 degfor side-slip angle). Four angle-of-attackmanoeuvres were successfully executed tostudy pitch damping. A detailed post-flightanalysis has just been completed with newexperiments and computations to check thedatabases. Figure 2 shows an example of aSchlieren picture in the S4 ONERA Modanefacility at Mach 10, together with correspondingpredictions using the in-house-developed Lorecode. Figure 3 compares experimentallyobtained oil-flow patterns with predicted skinfriction lines for the study of the local heating,using the same facility.
The ARD flight not only allowed the verificationof the use of ground-based facilities and theuse of CFD for databasing and design, but alsohighlighted some critical issues requiring furtherstudy and improvement, such as flight heat-fluxgauge integration and high-enthalpy wind-tunnel pressure and heat-flux data accuracyimprovement.
data are urgently required to remove anydoubts about the validity and accuracy of the CFD predictions and to confirm theextrapolation methodology. This is particularlyimportant for man-rated vehicles.
Today’s aerothermodynamic issues arediscussed below in the context of examplesfrom the different ESA Directorates.
Aerothermodynamic applications in theESA Manned Spaceflight and MicrogravityProgramme Thanks to ESA’s Manned Space andTechnology Research Programmes, Europeanexpertise in aerothermodynamics has beenadvanced considerably in recent years. Theflight of the Atmospheric Re-entry Demonstrator(ARD), and the challenging participation inNASA’s Crew Return Vehicle (X-38/CRV)programme with substantial Europeanhardware and software contributions, representmajor steps in this respect.
ARD ARD was flown successfully on Ariane-503 inOctober 1998. The objective was to test andqualify re-entry technologies and flight-controlalgorithms under real flight conditions, toachieve in-flight validation of design concepts,hardware and system capability, to validateaerothermodynamic prediction tools, to qualifythe thermal-protection system, to assessguidance, navigation and control laws, toassess parachute and recovery-systemperformance, and to study radio-communi-cation links during re-entry.
aerothermodynamic analysis
71
MUYLAERT 2/20/01 2:34 PM Page 3
Figure 3. ARD oil flowpatterns in the ONERA S4
facility at Mach 10(incidence angle 20 deg)
and the correspondingcomputed skin friction lines
Figure 4. Predicted X-38flow streamlines at Mach17.5 (incidence angle 40deg) combined with the
equilibrium radiative wall-temperature distribution
X-38/CRV The joint NASA/ESA/DLR X-38 project includesthe demonstrator V201 being assembled for aShuttle-carried hypersonic re-entry flightplanned for 2002. This partnership with NASAwill be carried over to the production of theoperational man-rated Crew Return Vehicle(CRV) for the International Space Station incollaboration with American industry as prime.
Some of the aerothermodynamic issues for theX-38 design are:– Stability and trimming: the influence of real
gas and viscous interaction effects on control-flap efficiency and heating.
– Roughness-induced boundary-layer transition,flap shear-layer transition and its influence onlocal heating.
– Micro-aerothermodynamic effects due to flowthrough hinges and gaps in rudders and flaps.
– Qualification testing of the thermal-protectionsystem in ground-based facilities and extra-polation to flight.
– Wall catalysis and radiation influencing heatingrates.
– Transonic dynamic derivatives for stabilitycontrol.
– Flight measurement techniques, including airdata system.
– Reaction and control system efficiencies.
To assess these issues, CFD is being heavilyused in defining wind-tunnel test conditions, ininterpreting the measured data, and finally forthe flight extrapolation.
Figure 4 shows some interesting flow patternson the windward and lee sides of the X-38vehicle at Mach 17.5 and 40 deg incidence. Itconfirms the predicted (Lore) increasedradiation equilibrium temperatures at theleading edges and at the flap corners,especially between the body flaps and at thebase end behind the control flaps. Figure 5shows the effect that the boundary layer haswhen it transitions from laminar to turbulent
r bulletin 105 — february 2001
72
MUYLAERT 2/20/01 2:35 PM Page 4
Figure 5. Predicted laminar and turbulent heat-flux distribution along the X-38’sdeflected body flap and a comparison with NASA LARC Mach 6 experiments
flow on the flap. A comparison is presentedwith experiments performed in the NASA LARC20-inch Mach 6 facility. The complexity andmultidisciplinary nature of the interactionsinvolved in the body-flap design are shown inFigure 6. Extensive testing is being conductedwithin the German TETRA programme usingthe L3K plasma facility at DLR in Cologne.Figure 7 shows a model set-up as tested underhigh-enthalpy conditions. Here again CFD isrequired for flight extrapolation, as the localconditions in the wind tunnel only partiallyduplicate those in flight.
The collaboration with NASA’s Johnson SpaceCenter has helped Europe to improve theunderstanding of such phenomena as windwardroughness-induced transition, based onShuttle lessons-learnt and extensive testing inNASA’s LARC Mach 6 facility. Roughness-induced transition correlations were developedand validated by properly designing theseroughness distributions on the windward sidesuch that the transition encountered in the windtunnel corresponds to that in flight. ThisEuropean collaboration with NASA is uniqueand all partners are looking forward tostrengthening the relationship through the
aerothermodynamic analysis
73
Figure 6. Sketch of complex flow-structureinteraction on the X-38 body flap
Figure 7. Surface-temperature distributions in the TETRA X-38 body-flap model withclosed and open gaps in the L3K facility at DLR in Cologne
Sketch of the X38 body-flap
3D Effects due to flow-structure interaction
– High temperature effects on heat-flux– Radiation cooling– Back radiation coupling– Heat conduction due to temperature
gradient inside body flap structure
MUYLAERT 2/20/01 2:35 PM Page 5
upcoming X-38/V201 hypersonic flight and theCRV programme.
Aerothermodynamic applications in ESAScience ProgrammesOne of the aerothermodynamic issuesassociated with satellites is plume impingementdue to the interaction of the propulsion systemwith the spacecraft’s surfaces. Improperlyengineered plumes not only produce pressureand frictional forces, but may also causecontamination or unacceptable heat loads. Toassess this computationally, a combination ofdifferent numerical methods is used: Navier-Stokes solvers for the continuum flow in thethruster nozzle, a Monte-Carlo direct simulationmethod for the near-transitional flow field, andfree-molecular-flow tools for the far field. Forroutine project design work, industry usesquick empirical models. Such models forplume/surface interaction are currently beingimproved using data obtained in the unique,ESTEC-supported STG simulation facility atDLR in Goettingen, which produces roughly 10 m3 of ‘real space conditions’. The interactionof the rarefied flow with the surfaces requiresseparate modelling.
Planetary-science missions with capsuleplanetary entry or Earth sample-return scenariosinvolve critical aerothermodynamic phenomena:– Direct entry using aerocapturing or aerobraking
techniques involves improved knowledge ofthe reaction and control system interactionswith the flow in transitional and continuumregimes.
– Thermochemical effects and radiation play adominant role in the shock layer and in thewake of capsules for TPS design. Enteringatmospheres of which the composition is notwell known makes the assessment evenmore complex.
– Wake-flow stability and wake-flow transitioneffects influence the payload shield designfor the capsule.
– For the higher capsule entry speeds, morecomplex phenomena have to be consideredin the layer between the bow-shock waveand thermal-protection system, such asradiation and ionisation including gas/surfaceinteractions, requiring knowledge of theappropriate material properties.
– The qualification of thermal-protection systemsin plasma facilities using gases other than airis non-trivial. In addition, in many cases thethermodynamic and chemistry databasesare incomplete or even non-existant.
Here also, CFD plays a major role in the designprocess. The validation is complex and requiresdedicated tests in shock tubes, shock tunnelsand plasma facilities using sophisticated
instrumentation. These only provide thedatabase for partial validation, because thefacilities cannot completely simulate the free-flight flow field around the capsules. Again, thevalidity of the CFD-based extrapolation needsto be checked against actual in-flight measureddata.
Aerothermodynamic applications in ESALauncher ProgrammesThe aerothermodynamic issues for launchersdiffer significantly from those for blunt-body re-entry vehicles. In general, Mach number(compressibility) and Reynolds number effects(viscous forces) are important parameters for ascent-type vehicles, whereas high-temperature effects and pressure forces aredominant for re-entry vehicles.
Ariane-5 The aerothermodynamic activities involved indesigning a launcher like Ariane-5 touch uponmany areas: overall drag assessment duringtake-off, unsteady buffeting loads assessmentat transonic speed, maximum steady-state loadestimations around Mach 2, booster separationand jet impact during staging, solid boosterradiation, local aerothermodynamics such aslocal heating at high Mach number around thebooster attachment bars, attitude-control-system plume contamination and performance,nozzle-induced side loads at start-up andsloshing in tanks during staging or payloadseparation.
Only a limited subset of the many interestingfluid-dynamics issues will be touched upon here:– Performance of the attitude control system:
Its qualification involved hydrazine tests atONERA Le Fauga for the verification ofpossible vaporisation inside the pipes. Becausethe test could not simulate vacuum conditions,CFD was used to extrapolate to flightconditions.
– Explaining peculiar measurements with thehelp of computational simulations: Anovershoot in heat flux measured in flightproved to be due to the sharp drop in thewall temperature at the locations of the heatsensors. Figure 8 shows the locations of thethermocouples on the Ariane-5 fairing, andthe temperature and corresponding heat fluxdistributions at those locations for two setsof flight conditions during ascent: thosecorresponding to Mach 3.7 and an altitude of29 km, and those for Mach 5.8 at an altitudeof 49 km. The predictions were made usingthe in-house-developed Sesmans code.
– The magnitudes of the buffeting loads in thebase region of the cryogenic tank (EPC) andon the Vulcain nozzle are a major concern.Unsteady, separated flow emanating from
r bulletin 105 — february 2001
74
MUYLAERT 2/20/01 2:35 PM Page 6
Figure 8. Comparison of computed and in-flight-measured heat flux on the Ariane-502 nose cone
Figure 9. Predicted unsteady velocity vectors in the base region of the Ariane-5model at Mach 0.7
the central core creates unsteady forces onthe Vulcain nozzle. The magnitude anddirection of these forces are influenced by 3Deffects originating from the protuberances,as well as from the solid boosters. Extensiveexperimental campaigns involving large-model testing in transonic facilities with andwithout plume simulation were carried out.The analysis has recently been augmentedwith experimental activities for the study ofpossible coupling between external flow andshock-separated flow in the nozzle (allexperiments in the transonic facilities arecarried out with cold jets, and extrapolationto flight involves an assessment of theinfluence of hot jets on the buffeting interaction).Figure 9 shows the predicted unsteadyvelocity vectors using the ESA-fundedEuranus code, highlighting the complexity ofthe flow. Figure 10 shows the Ariane-5 modelin the FFA transonic/supersonic facility (S4). Itis believed that the use of Large EddySimulations (LES) or eventually of DirectNumerical Simulation (DNS) will improve ourunderstanding by enhancing the analysis ofthe influence of the hot plumes.
– Ariane-5 loads: CFD can be used to assessthe pressure and heat loads and to updatethe launcher specification to reduce thestructural and thermal-protection-systemmass. To this end, CFD wind-tunnel flowsimulations are carried out to build upconfidence for flight computations. In-flightresults from several sensors at specificlocations provide the real flight data which,when used in combination with CFD results,allow the assessment of pressure and heatload. Figure 11 shows a typical 3D grid andpreliminary computational results (Lore) forMach 0.7 conditions in NLR’s transonicfacility (HST). The distribution of 3D pressureload in the base region is shown.
aerothermodynamic analysis
75
Heat Flux Comparison Ariane-5 Fairing Profile
MUYLAERT 2/20/01 2:36 PM Page 7
Figure 10. The Ariane-5model in the supersonic S4
tunnel at FFA
Figure 11. Surface mesh andpreliminary predictedpressure distributions
around an Ariane-5 model inNLR’s HST facility for Mach
0.7 conditions
– Vulcain-2 performance analysis: CFD wasused to analyse the boundary-layer separationand shock pattern during the flow start-upprocess in the nozzle. The challenge here isto include in the simulation the correctrepresentation of turbine exhaust gas (TEG)re-injection and the hydrogen dump cooling.The results explained the 3D heating patternsobserved in a series of hot-flow experimentsconducted at DLR in Lampoldshausen.Figure 12 shows the iso Mach contours(Lore) in the Vulcain-2 nozzle, the details ofthe flow structure near TEG injection and theH2 dump location, and the shock-inducedboundary-layer separation at the nozzle exit.
FESTIP Within ESA’s FESTIP Technology Programme,aerothermodynamic research has beenperformed in three main areas:
– Configuration analysis: Analysis of aerodynamiccoefficients was carried out on generic shapesusing numerical tools with different levels ofsophistication, taking the Experimental TestVehicle (EXTV) as the reference configuration.Force and moment bookkeeping data in theS4 FFA for the low-attack-angle ascentphase, with and without twin plume interaction,were analysed. Pressure-Sensitive Paint (PSP)data were recorded for comparison withCFD. Figures 13 and 14 show some typicalexperimental results with jets. The oil-flowpicture shows the complex interactions tothe lee side of the body flaps induced by thejets. The Schlieren photograph shows theembedded shock patterns at the location ofthe flap hinge influencing the overall trimmingof the vehicle.
– Critical-point analysis: Roughness-induced-transition experiments were conducted on a
r bulletin 105 — february 2001
76
MUYLAERT 2/20/01 2:36 PM Page 8
Figure 12. Predicted iso Mach lines for Vulcain 2 atdesign point at 115 bar with zoom of turbine
exhaust gas section and hydrogen dump slot
Figure 13. Schlieren picture of EXTV in the S4 FFAfacility at Mach 0.9, incidence angle 0 deg, nozzle
pressure ratio 10
Figure 14. Oil-flow visualisation on EXTV in the S4FFA facility at Mach 0.9, incidence angle 10 deg,
nozzle pressure ratio 10
generic configuration and compared withexisting correlations. Shock-wave boundary-layer interactions were studied for rampflows, and CFD was used to study scalingeffects, where in particular wall-temperatureeffects were addressed. As part of thisprogramme, base flow plume-interactionexperiments were also conducted at TU Delftand FFA for validation purposes. Theimportance of strut effects and the need forimproved, time-accurate turbulence modelswere stressed.
– Flight measurement techniques and flight-test analysis: The activities here focussed onthe definition of requirements for air datasystems for the Raduga D2 configurationand on the MIRKA flight analysis. Newexperiments in the plasma facilities at IRS(Univ. of Stuttgart) as well as in the LudwiegTube at HTG (Hypersonic TechnologyGoettingen) were performed with a MIRKAconfiguration for the study of catalycity andof the influence of real gas on shock stand-off distance. Numerical results in the windtunnel as well as under flight conditions werederived for MIRKA. These confirmed that in-flight catalytic experiments are feasible onsimple ballistic configurations.
FLTP To improve understanding of the issues relatedto launch-vehicle reusability and to enhanceEuropean technology in this field, the FutureLaunchers Technologies Programme (FLTP)was initiated as an ESA optional programme.Here we are focussing on the critical pointsfrom previous programmes that have not yetbeen completely solved: – Increased heating due to roughness-induced
boundary-layer transition will be investigatedand shear-layer transition validationexperiments will be carried out. CFD will beused to study scaling issues and hot-walleffects.
– Plasmatron experiments will be carried out tostudy the catalycity and compared withlaboratory-obtained O2, NO and N2 catalyticrecombination reactions. CFD will be used tobridge the gap and to report on the accuracyof the semi-numerical methods as presentlyused in the plasmatron.
aerothermodynamic analysis
77
MUYLAERT 2/20/01 2:37 PM Page 9
Figure 15. Meteosat SecondGeneration (MSG) plume-
impingement numericalanalysis using Navier Stokes
predictions for the nozzleand Monte Carlo
simulations for the plumeflow
– Local aerothermodynamics effects will beinvestigated such as flap/gap flow, with theemphasis on scaling.
– Base flow experiments, with and without jetinteraction, will be performed, with theemphasis on hot-plume effects. Understandinghot-plume effects is crucial not only for baseflow pressure recovery and heating, but alsofor unsteady buffeting effects and nozzle flow separation/external flow interactionassessment.
Aerothermodynamics in ESA ApplicationProgrammesA typical example of plume-impingementanalysis for an Application Programme isshown in Figure 15, for the MSG mission. Theback flow emanating from the main 400 Nrocket-engine nozzles impinges on thesatellite’s external ring and on its base. Theheat shields around each of the two nozzlesprotect the satellite base region againstradiation and against convective heating. Acoupled Navier-Stokes (in-house-developedYPANS code) and Direct Simulation MonteCarlo solver (ITAM/ Smile code) has been usedto compute the total energy flux at criticallocations. This analysis involved axisymmetriccomputations; 3D computations are planned topredict the heat flux to be measured in flight.
Aerothermodynamic research activities inESAThe Agency has set up TechnologyProgrammes (GSP, TRP, GSTP) in order toinitiate novel developments and to assureknowhow continuity, and to advance analysisand experimental capabilities.These activities are intended toprepare to meet the technologyneeds for future programmes andadvance our capabilities to allowindustry to stay at the cutting edgeof technology. The (non-exhaustive)list of aerothermodynamic researchactivities includes:
– Gap heating, using data from the Japanesesuborbital re-entry demonstrator Hyflex: Acombined numerical and experimental activityhas been set up using the DLR L3K facility,where a set of instrumented tiles are beingtested which are identical to those used inflight (Fig. 16). The objective is to achievewind-tunnel conditions such that the localconvective and radiative heat fluxes in thegaps are as close as possible to those inflight. Wind-tunnel and flight flow fields arebeing predicted with CFD, taking into accountthe 3D effects in the gaps as well as the heatconduction into the material. The resultsobtained from the analyses will identify wherefurther investigations in the flow /material-interaction area are needed.
– Plasmatron measurement techniques: Non-intrusive measurements will be developedand calibrated to provide a direct means ofmeasuring the species concentrations in theboundary layer in front of a model. This methodwill be compared with the semi-numericalmethods currently being used in plasmatronapplications to assess recombinationcoefficients.
– Hot-plume testing: Retrofitting of an existingH2/O2 propulsion stand is planned to studythe influence of hot plumes on the basepressure and heating of launchers.
– Buffeting: Experimental and numerical studiesof base-flow buffeting on simple and complexAriane-5 models are planned, including cold-jet effects.
– Nozzle flow-separation control device:Experimental and numerical flow-separationstudies will be conducted on different nozzle
r bulletin 105 — february 2001
78
MUYLAERT 2/20/01 2:37 PM Page 10
Figure 16. Hyflex tilesinstrumented with as-flownsensors tested in the L3KDLR facility in Cologne
Figure 17. The IRDT reentryconfiguration
Aerothermodynamics has emergedas a key discipline for the design andqualification of advanced launchers,re-entry vehicles, and planetaryprobes. It requires enhancements inmultidisciplinary techniques which,thanks to the rapid growth incomputing power, will be increasinglyused in the future. The Agency isworking towards continued and well-directed research with flightdemonstrators to advance Europe’scomputational and experimentalcapabilities for future spaceprogrammes. Continuation of such
activities in Europe is essential to remain at thecutting edge of technology for spacetransportation.
These efforts will be supported by co-ordinating European activities and promotingcloser collaboration between universities,research establishments and industry. Thesuccess of this challenging undertakingdepends upon support from all of the nationsinvolved. Continued international cooperation,such as the partnership with NASA in the CRVProgramme, will only be possible if Europecontinues to enhance its aerothermodynamicknowhow and expertise, which includes theavailability of verification facilities and flightdemonstrators.
Acknowledgement The authors are grateful to C. Stavrinidis forreviewing this article; to J. Steelant for his in-depth contributions to the Vulcain analysis; toG. Markelov for his substantial contributions to the DSMC analysis for MSG; and to G. Tumino for his work associated with theScirocco project. They thank R. Molina (X38),M. Steinkoph (ARD) and M. Toussaint forpermission to show the ‘project support’figures. Thanks also go to E. Luparini for hisassistance in preparing the figures. s
shapes such as the classical bell-type, dual-bell, extendable and external-expansionnozzles in order to understand and controlnozzle flow separation.
– In-flight research: The objective is to performa feasibility study for in-flight research usinggeneric configurations to study transition,catalycity and shock boundary-layerinteraction. The study will also focus on thecorresponding wind-tunnel tests to representflight, and on improvement of the accuracyof flight measurement techniques and theirintegration into the thermal-protection system.
– Inflatable Re-entry and Descent Technology(IRDT): A flight experiment was performed in 2000, which was supported by theEuropean Commission through the ISTCprogramme. Astrium carried out thisprogramme in close collaboration withBabakin Space Centre (Lavochkin). One ofthe objectives was to evaluate IRDT’s potentialas an independent, low-cost payload-returncapability for experiments conducted on theInternational Space Station (ISS). Thesuccessful suborbital flight in February 2000confirmed the technology’s potential (Fig. 17;see also ESA Bulletin No. 103, August 2000).Another flight, initiated by the Directorate ofManned Spaceflight and Microgravity, and aprecursor flight are planned for March andAugust 2001, respectively. Near-orbital entryconditions will be achieved for full validationof the concept.
ConclusionsThis article has discussed some of the criticalaerothermodynamic issues inherent in thedesign of re-entry space vehicles andlaunchers, as well as reviewing the analysis andtest results obtained to date. The importance offlight-testing for the validation of methods andprocedures for the extrapolation of resultsobtained from ground-based facilities has beenhighlighted. In particular, such flight data areneeded to establish real confidence both in thecomputational fluid dynamics and theunderlying physical modelling.
aerothermodynamic analysis
79
MUYLAERT 2/20/01 2:37 PM Page 11
