DEVELOPMENT OF DETAILED CHEMISTRY MODELS FOR BOUNDARY LAYER CATALYTIC RECOMBINATION

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1 DEVELOPMENT OF DETAILED CHEMISTRY MODELS FOR BOUNDARY LAYER CATALYTIC RECOMBINATION G. Beas-Chatzigeorgis 1,2, P. F. Barbante 3, and T. E. Magin 4 1 Poitecnico di Miano, Department of Mathematics, P.zza Leonardo da Vinci 32, Miano, Itay 2 von Karman Institute for Fuid Dynamics, Aeronautics and Aerospace Department, Chaussée de Wateroo 72, 1640 Rhode-Saint-Genèse, Begium, Emai: georgios.beas.chatzigeorgis@vki.ac.be 3 Poitecnico di Miano, MOX, Department of Mathematics, P.zza Leonardo da Vinci 32, Miano, Itay, Emai: paoo.barbante@poimi.it 4 von Karman Institute for Fuid Dynamics, Aeronautics and Aerospace Department, Chaussée de Wateroo 72, 1640 Rhode-Saint-Genèse, Begium, Emai: thierry.magin@vki.ac.be ABSTRACT During the (re-)entry phase of a space vehice, the gas fow in the shock ayer can be in a state of strong therma non-equiibrium. Under these circumstances, the popuation of the interna energy eves of the atoms and moecues of the gas deviates from the Botzmann distribution. A substantia increase of the heat fux transferred from the gas to the vehice is possibe, as the therma protection system of the vehice acts as a catayzer. The objective of the paper is to show how therma non-equiibrium and cataysis can jointy infuence wa heat fux predictions. In order to study therma nonequiibrium effects a coarse-grained State-to-State mode for nitrogen is used couped with a phenomenoogica mode for cataysis. From the numerica simuations performed, an important effect on the heat fux has been observed due to the interaction of cataysis and therma nonequiibrium at the wa. Key words: cataysis, gamma mode, state-to-state modes, therma non-equiibrium, accommodation coefficient, stagnation ine. 1. INTRODUCTION The design of the therma protection system for a spaceship during an atmospheric entry is a very chaenging task due to the muti-physics phenomena occurring in the shock ayer of the space vehice [1]. These phenomena incude strong deviation from thermochemica equiibrium [22], radiative heating [17] and gas-surface interaction (cataysis and abation) between the vehice s surface and the surrounding gas [6]. These phenomena are strongy couped between each other and this makes the prediction of the fow-fied properties very difficut. Currenty, most researchers try to dea with each of these phenomena separatey or with simpified couping strategies. For a reevant fraction of the re-entry trajectory the fowfied behind the shock wave and in the boundary ayer is in a state of therma non-equiibrium; the popuations of the interna energy eves of atoms and moecues deviates from the Botzmann distribution. A substantia increase in the heat fux can observed as the cataycity of the wa of a re-entry vehice increases with wa temperature [5, 26]. Currenty, most of the simuations performed by the community assume therma equiibrium in the fow fied. The objective of this contribution is to study the joint effect of therma non-equiibrium and cataysis on the predicted heat fux. 2. PHYSICAL MODEL Therma non-equiibrium is studied with a state-to-state rovibrationa specific nitrogen mode deveoped by the NASA Ames Research Center [12]. The mode can simuate fows that depart from Botzmann equiibrium, ike strongy compressing, expanding and boundary ayer fows [21]. Each interna energy eve is assumed to be a distinct pseudo species. Chemica reactions are the mechanisms responsibe for transforming one of these pseudo species to another one. Even though state-to-state modes are more accurate than muti-temperature ones, they ead to a drastic increase of the computationa cost. A possibe strategy to reduce the the computationa cost is presented in the paper Energy Leves The nitrogen mode has 9390 different rovibrationa eves, which can be spit into two categories, bound (B) and predissociated (P). The bound eves are the eves whose tota energy is ess than the dissociation energy (9.75eV ) of nitrogen moecue in its eectronic ground state. The predissociated eves are the eves whose energy is higher than the dissociation energy reative to the

2 first rovibrationa energy, but ower than the rotationa dependent centrifuga barrier [12]. A simuation with a the 9390 different eves woud have a huge computationa cost. In order to reduce the computationa cost coarse-grained modes are deveoped. The reduction strategy that chosen for this project is the Uniform Rovibrationa Coisiona bin mode (URVC) [16]. The rovibrationa energy eves are sorted in an increasing energy eves adder. Then, this adder is divided into two parts, the first one containing ony the bound eves and the second one ony the predissociated eves. Lasty, each of these two regions is divided with equa energy spacing: E B = 2E fn N B, E P = E max 2E fn N P (1) where E fn is the formation energy of N and E max the energy of the ast energy eve of N 2. N B and N P are the number of bound and predissociated bins, which can be chosen freey. The higher their number the better is the fideity of the mode. Here we have chosen N B = 7 and N P = 3. A sensitivity anaysis has been performed in [18] and it was shown that no big effect on the heat fux was observed going from 10 bins to 100 bins. The popuation distribution, n, of the energy eves contained in each bin is chosen to be uniform: n = g i n i (2) i g i where g i is the degeneracy of eve i and n i its popuation. The number density n k of each bin is n ; its degeneracy g k is g. The average energy of bin k is equa to: Ē k = 1 g g i E i (3) where E i is the interna energy of the i th eve. Aternative strategies of mode reduction can be found in [15, 18]. The advantages of the URVC mode are the simpe impementation, the fact that the average energy of the bins is not a function of the thermodynamic state and good quaity of the resuts, especiay at high temperatures. A non equa energy spacing for the bins might aso improve the quaity at ower temperatures. The main disadvantage of this mode is that it cannot reach Botzmann equiibrium at a fine-grain eve. As a post processing resut an interna temperature (T int ) has been defined by soving the foowing equation: k n kēk k = Ēkg k exp(ēk/k B T int ) n N2 k g (4) k exp(ēk/k B T int ) Physicay, it represents the temperature that woud exist in the fow fied if the interna energy eves of N 2 were popuated in a Botzmann way, with the mixture having the same amount of interna energy Reaction Mechanism i In a (N( 1 S u ) N 2 ( 1 Σ + g )) mixture two kind of interactions can exist. The first one is the coision between nitrogen atoms and moecues, the second one the coision between nitrogen moecues. In the present mode ony the first category of coisions has been considered. The second one has not been taken into account because ony a portion of a the possibe transitions rates are currenty avaiabe [20]. Spontaneous dissociation was aso assumed to be negigibe [18]. The tota number of reactions that are needed to describe the possibe transitions from one rovibrationa eve to any other or to dissociated nitrogen, with the third body being a nitrogen atom, is of the order of The reactions beong to two different categories, the third body dissociation reaction and the ineastic transitions reaction between rovibrationa eves: N 2 () + N kdis k rec N 2 () + N kin k in N + N + N (5) N 2 ( ) + N (6) The forward reaction rates are computed with the quasicassica trajectory (QCT) method, using potentias cacuated from ab-initio quantum mechanics computations [12]. The backward reaction rates are computed with the microreversibiity principe. For the URVC bin mode the same reaction categories appy, but on each singe bin. The forward reaction rates of bin k are obtained from the formuas: k dis k = 1 g k g k dis k in k k = 1 g k k, g k in (7) The backward reaction rates are not connected through the micro-reversibiity principe to the forward ones; they are computed using the equiibrium constant which is obtained by minimizing the Gibbs free energy of the bins. In this way equiibrium is obtained at a bin eve. In order to correcty compute the minimum Gibbs free energy, even without eectronic energy, the degeneracy of the first eectronic eve of N is required, that for the state-to-state mode is equa to GOVERNING EQUATIONS The dynamica evoution of the bins is governed by the Navier-Stokes equations: ρ i t + (ρ iu + j i ) = ω i, (8) ρu t + (ρu u + pi + τ) = 0, (9) ρe t + (ρuh + τu + q) = 0. (10) ρ i is the partia density of bin i, ρu and ρe are momentum and tota energy of the whoe mixture. j i is the diffusion fux and ω i is the chemica production/destruction term of bin i. The identity matrix is symboized with I, p is the mixture pressure, τ is the stress tensor and q is the heat fux. If Eqs. 8 are summed up over a the species

3 in the mixture, the tota continuity equation wi be obtained, since i ρ i = ρ. For the state-to-state approach, one distinct continuity equation for each bin is soved. Each bin is supposed to behave as a perfect gas Transport Properties In order to cose the Navier-Stokes equations (Sec. 3) that govern the bins dynamic, expressions for diffusion fux, stress tensor and heat fux shoud be obtained. The transport properties are computed using the Mutation++ ibrary, deveoped by Scoggins and Magin [24] at the von Karman Institute for Fuid Dynamics. In the computation of the transport properties it is assumed that the eastic coisions cross sections are the same for a interna quantum states and ineastic coisions have no infuence. The diffusion fux is computed with the Stefan-Maxwe equations (there is one of these equations for each bin): M ρ k ( xi j k M k D ik x ) kj i = x i (11) M i D ik where x i is moe fraction gradient of bin i. D ik is the binary diffusion coefficient. Stress tensor reads cassicay: τ = µ[ u + ( u) T 2 ui], (12) 3 where µ is the shear viscosity. Heat fux reads: q = λ T + i h i j i (13) where λ is the therma conductivity associated with the transationa temperature T of the gas species and the second term is the diffusive heat fux, which wi be referred as q diff Numerica soution The above formuation has sti a high computationa cost because of the subdivision into bins. For this reason a specia formuation of the Navier-Stokes equations, caed dimensionay reduced Navier-Stokes equations (DRNSE) [13], that simuates the fow fied ony on the stagnation ine of the re-entry vehice is soved. The Navier-Stokes equations are written in spherica (r, θ, φ) coordinates. The fow is assumed to be axisymmetric and therefore u φ = 0 and / φ = 0. The symmetry of the fow impies that u r, p, T and ρ i are symmetric (cosine) with respect to the stagnation ine axis (ocated at θ = 0) and u θ is antisymmetric (sine) with respect to it. Furthermore, the Newtonian theory for pressure distribution of hypersonic fows is assumed. Finay, by taking the imit of θ 0 the DRNSE equations [13] are obtained. The DRNSE system of equations is soved using the finite voume method in space, with an impicit Backward Euer method in time [11]. Detaied information about the numerica method can be found in [18]. 4. CATALYTIC WALL The surface of the therma protection system can act as a catayzer with respect to the gas mixture chemica species that impinge on it. If this is the case, the recombination of dissociated species is promoted and the chemica energy reeased increases the heat oad of the vehice. In order to mode this phenomenon, a correct boundary condition shoud be imposed at the wa surface for the mixture s chemica species. For a cataytic wa at a steady state, the mass of each species produced or destroyed by surface reactions shoud be equa to the diffusion fux of the species at the wa. Hence: j i n w = ẇ i,cat (14) where n w is the unit vector norma to the surface and ẇ i,cat is the mass of species i produced or destroyed per unit of area and unit time. The right hand side is modeed using a phenomenoogica approach, the γ mode, widey used in the aero-thermodynamics community [4, 7]. The recombination probabiity γ i is defined as: γ i = M i,rec M, (15) i where M i is the fux of species i impinging the surface and M i,rec is the fux of species recombining at the surface. A fuy cataytic wa has γ i equa to 1, which means that a the partices of species i impinging the surface recombine at the wa. γ i equa to 0 means that no reaction takes pace and corresponds to a non-cataytic wa. Anything between these two extreme cases is a partiay cataytic wa. Knowing the probabiity γ i, the right hand side of Eq. 14 is equa to [4]: ẇ i,cat = γ i m i M i (16) When the transationa energy modes of gas species cose to the wa have a Maxweian distribution function and there is no temperature sip, the impinging fux, M i, is equa to [4]: M i = n ktw i (17) 2πm i where T w is the wa temperature. For the state-to-state mode specific wa recombination reactions are considered for every different rovibrationa bin, each one with their own recombination probabiities γ i : N + N γi N 2 (i). (18) Since in iterature there are no avaiabe vaues for γ i, three cases are considered. In the first case γ i is assumed to be equa for every bin. γ i is obtained by dividing a goba recombination probabiity γ by the number of bins considered in the mode. For this contribution, γ = 0.01 and because we consider 10 bins γ i = This case wi be referred as the equiprobabe cataytic case. In the second case, it is assumed that recombination occurs ony in the ower energy bin, which means that γ i=1 = 0.01

4 and the others are equa to 0. This case is caed the ower cataytic case. In the third case recombination occurs ony to the highest energy bin. This wi be the upper cataytic case. As a concuding remark, it shoud be mentioned that the purpose of the paper was not to find a rigorous vaue for recombination probabiities. The aim was to check how the heat fux is affected in each case. In the future, there are pans to extract from a finite rate chemistry and a dynamica Monte Caro approach more accurate recombination probabiities γ i and coupe them with the bin mode [8, 25, 9]. Temperature [K] Temperature Profie 4.1. Accommodation Coefficient The recombination of atoms at the surface reeases their chemica energy. Nonetheess, not a of this energy shoud transferred to the surface. Some of it may be saved within the created moecue as interna energy (rotationa, vibrationa or eectronic). One of the aims of using stateto-state modes for cataysis is to determine how much of this energy is reeased to the wa and how much is saved as energy of the moecues. A suitabe parameter, the chemica energy accommodation coefficient β, is introduced [10]: β = q diff i ω i,cat H i,r (T wa ), (19) where q diff is the diffusive heat fux and H i,r (T wa ) is energy reeased by the recombination reaction that invoves bin i at therma equiibrium. The β coefficient is non-dimensiona and can take vaues between 0 and 1. β = 0 means that none of the energy reeased during the cataytic recombination is transferred to the wa and β = 1 means the opposite. Researchers often use the product of β and γ coefficients defining an overa effective cataytic probabiity, γ eff, in order to characterize the cataytic efficiency derived from experiments [5]. In this paper the chemica energy accommodation coefficient is expicity determined. Simiar approaches for the determination of the accommodation coefficient can be found in [3]. 5. RESULTS The fow on the stagnation ine around a spherica bunt body of radius r = 0.4 m is studied. The free stream pressure is equa to p = 44 P a, the temperature is T = 300 K and the free stream veocity is equa to m/s (M = 28.33). Because, ony N 2 N coisions are considered, the free stream is seeded with 2.8% per moe of atomic nitrogen. The wa is considered in equiibrium with temperature equa to 2000K. This temperature is reativey high for cataytic studies, nonetheess it has has been chosen for vaidation purposes in order to have a test case consistent previous ones [18, 19]. In Fig. 1 the temperature profies for the non-cataytic Distance from Wa [m] Figure 1. State-to-state simuations for N in for the noncataytic case. Temperature profie aong the stagnation ine. (unbroken ine): Transationa temperature; (dashed ine): Interna temperature. case aong the stagnation ine are presented; transationa and the interna (see Eq. 4) temperatures are shown. The free stream is not in therma equiibrium, because at ow temperatures the URVC mode stores an excess of energy in the first bin; this effect fades away once the temperature increases. An area of strong therma non-equiibrium is observed across the shock wave. At a distance of x = 0.02 m from the wa the two temperatures becomes practicay equa. The two temperature are very cose to each other inside the boundary ayer, except at the wa x = 0 m. The interna energy bins popuation inside the boundary ayer, cose to the wa, is potted in Figs. 2 and 3 in terms of their moar fractions divided by the bin degeneracy. In Fig. 2-top the non-cataytic case is shown. Inside the boundary ayer, up to a distance from the wa equa to x = m, the energy eves have a Botzmann distribution, as it is seen by the straight ine in the ogarithmic pot, which changes its sope because of the decrease in temperature due to the infuence of the wa. At x = m the Botzmann character starts to be ost; the non predissociated higher energy states get more and more popuated, whie the predissociated states are depeted. This effect is maximized at the wa. Fig. 2-bottom shows the distribution of interna energy bins for the ower cataytic case. The behaviour is simiar to the non-cataytic case, except that the first bin is overpopuated, because the wa promotes recombination of nitrogen atoms into moecues beonging to the first bin. Fig. 3 shows the distribution of the interna energy bin for the, equiprobabe (top) and upper cataytic (bottom) cases. The two cases show a simiar trend. Up to a distance of the order of x = m from the wa the eves are popuated with a Botzmann distribution. Very cose to the wa the Botzmann distribution does not hod any more and the higher energy bins are overpopuated in both cases; cataysis promotes therma non-equiibrium

5 10 6 Energy Bin Distribution Energy Bin Distribution Energy Bin Distribution Energy Bin Distribution Figure 2. Distribution of the interna energy bins cose to the surface for the non-cataytic (top) and ower (bottom) case. (x: x = 0 m; o: x = m; +: x = m; diamond: x = m; square: x = m). at the wa. For the sake of comparison the distributions of energy bins at the wa, for a the four cases, are potted together in Fig. 4. Fig. 5 depicts the moar fraction of N aong the stagnation ine for the four cases. In the non-cataytic case (unbroken ine) the recombination is due ony to the recombination reactions in the gas phase. The recombination predicted by the present mode is ower compared to the one predicted by the Park mode [18, 23]. In the ower cataytic case (dotted-dashed ine) the nitrogen moar fraction is further reduced because of wa recombination. This does not happen for the equiprobabe and upper cataytic cases, where the popuations of the N atoms are higher. This is mainy due to two combined effects. First of a, it can be seen in Fig. 5 that the boundary ayer is ess thick in the equa and upper cataytic cases. This eads to a reduced recombination, because of the ess time avaiabe for the reactions. Secondy, since in these two cases nitrogen moecues are preferentiay formed Figure 3. Distribution of the interna energy bins cose to the surface for the equiprobabe (top) and upper (bottom) cataytic case. (x: x = 0 m; o: x = m; +: x = m; diamond: x = m; square: x = m). in high vibrationa states, they are much more ikey to dissociate after desorption and to reease their interna energy into transationa one, a phenomenon known as quenching. This effect can be inferred from the temperature profies inside the boundary ayer. Fig. 6 shows the transationa and interna temperature profies in the boundary ayer for the four cases. The profies of the non-cataytic and ower cataytic cases are very simiar and the same happens for the equay and fuy cataytic case. The transationa temperature gradient increases going from non-cataytic to the upper cataytic case, because highy excited desorbed moecues transfer their interna energy to transationa one. In Fig. 6-bottom the interna temperatures of the fow fied are presented. In the non-cataytic case the interna temperature at the wa is equa to 2252 K which is higher than the imposed transationa temperature. Therefore, the assumption of therma equiibrium at the wa is not vaid and this effect

6 Energy Bin Distribution 1 Moar Fractions of N Moar Fraction Distance from Wa [m] Figure 4. Comparison of distributions of interna energy bins for the four cataytic cases. x: Non-cataytic case; +: Lower cataytic case; o: Equiprobabe cataytic case; square: Upper cataytic case. shoud be taken into consideration in muti-temperature simuations. As the wa cataycity increases the interna temperature increases too and it reaches the highest vaue of 4384 K for the upper cataytic case. These resuts are consistent with simiar ones avaiabe in iterature [18]. Heat fuxes are shown in Tab. 1. The wa heat fux for the non-cataytic case is 3.02 MW/m 2 ; the diffusive heat fux contribution is zero since it is a non-cataytic wa. In the cataytic cases heat fux is the sum of the conductive contribution q con = λ T and the diffusive one q con = i h i. For the ower cataytic case the conductive heat fux increase due to the increase in the sope of the temperature. The diffusive heat fux is aso high and of the order of magnitude of the conductive heat fux. As we impose equiprobabe recombination or recombination to the upper energy bin the heat fux greaty increases due mainy to the contribution of the conductive heat fux. The diffusive heat fux though decreases, because, as aready mentioned in the comments to Fig. 5, there is itte net recombination of nitrogen atoms. The resuts shown in this paragraph for our nitrogen state-tostate mode agree quaitativey with the ones obtained for a vibrationa specific oxygen mode in [2, 14]. The vaues of the β coefficient computed accordingy to Eq. 19 are shown in Tab. 2. In the non-cataytic case the β coefficient cannot be defined. In the cataytic cases, as Figure 5. Comparison of N moar fraction for the four cases. unbroken ine: Non-cataytic case; dotteddashed ine: Lower cataytic case; dashed ine: Equiprobabe cataytic case; dotted ine: Upper cataytic case. aready expained, β can take vaues between 0 and 1. In the ower cataytic case ony a sma part of the recombination energy is transferred to the interna energy of the desorbed N 2 moecue. Most of the energy is therefore transferred to the surface and for this reason we have β = , very cose to one. This is the maximum vaue attained by the β coefficient. In the upper cataytic case, where a of the N atoms recombine into the highest energy bin of N 2, the β coefficient is equa to meaning that very sma part of the recombination energy is directy transferred to the wa. The equiprobabe cataytic case stays in between with β = In the ast two cases, even though ony a sma part of the recombination energy is directy transferred to the surface, the heat fux increases substantiay, because the quenching phenomenon enhances the conductive part of the heat fux. Therefore, even though the β coefficient has an interesting physica meaning, it cannot be used as an accurate indicator for the tota heat fux transferred to the wa, but ony as an indicator of the diffusive (reactive) portion of heat fux directy transferred to the wa. Tabe 1. Heat fux [MW/m 2 ] for the URVC bin mode. q tota q con q diff Non-cataytic Lower cataytic Equa cataytic Upper cataytic Tabe 2. β coefficient and T int [K] for the URVC bin mode β T int Non-cataytic 2252 Lower cataytic Equa cataytic Upper cataytic

7 Temperature [K] Temperature [K] Transationa Temperature Distance from Wa [m] Interna Temperature Distance from Wa [m] ergy eves, with a specuar decrease of the β coefficient. Nonetheess the conductive heat fux is strongy enhanced by the quenching phenomenon, eading, in the end, to a net increase of the overa heat fux. These resuts are in agreement with previous iterature data. As a future work, the Botzmann rovibrationa coisiona mode can be used in order to remove some of the weak points of the Uniform rovibrationa coisiona mode. N 2 N 2 coisions shoud aso be incuded, as we as eectronic energy eves beyond the ground one. Extension to a fu air mixture incuding the O 2 and NO moecues woud be aso of interest, making the comparison to experimenta resuts easier. As far as the treatment of the wa is concerned, treating cataysis with a microkinetic mode is in view. The atter mode can be couped directy with a fow sover or used as a test bench for obtaining more accurate vaues for the cataytic recombination probabiity γ. Vaidation of the resuts is aso necessary by comparing the simuations with experimenta resuts on cataysis, performed at von Karman Institute or by other experimenta teams. ACKNOWLEDGEMENTS The authors are gratefu to James B. Scoggins for his time and support concerning the usage and further deveopment of the Mutation++ ibrary, to Erik Torres for his toos for the reduction of the fu NASA mode into the Uniform Rovibrationa Coisiona one and to Aessandro Munafò for the stagnation ine code. Research of G. B. C. and T. E. M. is sponsored by the European Research Counci Starting Grant # Figure 6. Comparison of the transationa and interna temperature profies for the four cases. (unbroken ine): Non-cataytic case; (dotted-dashed ine): Lower cataytic case; (dashed ine): Equiprobabe cataytic case; (dotted ine): Upper cataytic case. 6. CONCLUSIONS In this paper the joint effects of therma non-equiibrium and cataysis have been studied on the stagnation ine fow fied of a re-entry body. The Uniform Rovibrationa Coisiona coarse-grained mode of nitrogen has been used. The coarse-grained mode is based on an ab-initio rovibrationa nitrogen mode deveoped at NASA Ames research center. The gamma mode has been used in order to simuate the cataytic properties of the re-entry body therma protection system and it has been extended in order to account for the rovibrationa mode. The fow fied has been modeed by soving the Navier-Stokes equations using an impicit Finite Voume method. Heat fux is strongy affected by the mutua interaction of cataysis and therma non-equiibrium. The diffusive heat fux decrease when cataysis acts ony on the higher en- REFERENCES 1. J.D. Anderson. Hypersonic and High-Temperature Gas Dynamics. AIAA Education Series. American Institute of Aeronautics and Astronautics, I. Armenise, M. Capitei, C. Gorse and M. Rutigiano. Nonequiibrium vibrationa kinetics of an O 2 /O mixture hitting a cataytic surface. Journa of Spacecraft and Rockets, 37:3: , M. Baat-Pichein, V.L. Kovaev, A.F. Koesnikov and A.A. Krupnov. Effect of the incompete accommodation of the heterogeneous recombination energy on heat fuxes to a quartz surface. Fuid Dynamics, 43(5): , P. F. Barbante. Accurate and Efficient Modeing of High Temperature Nonequiibrium Air Fows. PhD thesis, Université Libre de Bruxees, O. Chazot. Experimenta studies on hypersonic stagnation point chemica environment. RTO-EN-AVT- 142 von Karman Institute Lecture Series: Experiment, Mode and Simuation of Gas-Surface Interactions for Reactive Fows in Hypersonic Fights, 2007.

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