Detailed and simplified kinetic schemes for high enthalpy air flows and their influence on catalycity studies
Résumé
The thorough understanding of the formation and the relaxation of the plasma produced in the shock layer developed during the re-entry of a spacecraft in the upper layers of the earth's atmosphere is crucial in order to prevent damaging of its outer surface. Among the different points to be studied, the chemical aspects are particularly important: the mechanical characteristic time scale of the flow being short, the flow is indeed in chemical nonequilibrium. In addition, the inner storage of energy of the different species of the flow leads to other mechanical behaviors than those observed in classical low temperature flows. These nonequilibrium effects have to be taken into account accurately in codes devoted to the study of the interaction between the plasma and the surface. In this work, we propose to focus our attention on the kinetics of an air plasma under nonequilibrium conditions by discussing the elaboration and the results of a collisional-radiative CR model taking into account 13 species and numerous excited states and working over a wide range of pressure and temperature. We will comment in details the elaboration of a reduced kinetic scheme derived from the CR model. First, we will present the influence of this scheme on the crossing of a 1D shock front. Second, we will draw several lessons from the results of a 1D code simulating the stagnation point boundary layer near the wall of the spacecraft working either with our own reduced kinetic scheme or with classical schemes (schemes proposed by Park, or Dunn & Kang or Losev) usually implemented in high enthalpy air flow codes.