Transferts radiatifs dans les écoulements hypersoniques de rentrée atmosphérique terrestre

Abstract : Thermal protection design of spacecraft requires the knowledge of heat fluxes at the vehicle surface. For the kind of atmospheric entry considered in this work (earth reentry at 10-12 km/s or more), radiation significantly contributes to the surface heating. We present in this study, the development and the use of models and numerical tools to predict radiative transfers in the shock layers encountered in earth re-entry in nonequilibrium conditions and multi-dimensionnal geometry. First of all, we have formulated, in a line by line approach, the expressions of radiative properties of N2-O2 plasmas in nonequilibrium conditions. This formulation is suitable for a multi-temperature and/or a electronic state to state description of the thermal nonequilibrium. It has been used to simulate the test case FIRE II in order to determine radiative intensity at the stagnation point for four trajectory points. Results show a good agreement with flight data for different spectral measurement ranges form IR to UV, except for the trajectory point in strong nonequilibrium conditions. Calculations show moreover that VUV spectral range contributes significantly to the intensity at the wall and that taking into account chemical nonequilibrium is crucial. An approximate model of radiative properties has been developed on the basis of a statistical narrow band (SNB) model for optically thick (in our application) electronic molecular systems, of a box model for optically thin electronic molecular systems and continua, and of a line by line approach for atomic lines. The use of the hybrid model has required a suitable RTE formulation to take into account nonequilibrium and spectral correlations. Systematic validations of the SNB model for each contribution have been carried out. The hybrid model has then been validated on the test case FIRE II against line by line calculations. The hybrid model has been implemented in the ASTRE radiative solver, which is based on a Monte Carlo approach. The implementation has been validated in comparison with a ray tracing method on a tangent slab configuration. 3D radiative calculations have been then carried out on the test case FIRE II. Results show discrepancy of 10-15 % on the fluxes at the stagnation point with results obtained in the tangent slab approximation which is usually used in the litterature. The developed tools allow to obtain relatively well converged (5 %) results in tri-dimensional geometry (100000 cells) with a reasonable CPU time enabling to consider coupled calculations in futur works.
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Autre. Ecole Centrale Paris, 2009. Français. 〈NNT : 2009ECAP0026〉
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Jean-Michel Lamet. Transferts radiatifs dans les écoulements hypersoniques de rentrée atmosphérique terrestre. Autre. Ecole Centrale Paris, 2009. Français. 〈NNT : 2009ECAP0026〉. 〈tel-00453309〉



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