Numerical simulation of stagnation line nonequilibrium airflows for reentry applications

We study the stagnation point boundary layer of high enthalpy subsonic flows obtained in inductively coupled plasma torches, aiming at determining the catalytic properties of materials for reentry applications. Simple recombination processes are often considered with the same recombination probability at the wall. In this work, a phenomenological model has been used to describe more accurately the gas-surface interaction. This model shows that the recombination processes are strongly dependent on the wall temperature, the concentration of the different species close to the wall, and the free sites available on the surface. Moreover, the wall is found to be noncatalytic at low temperatures. Then, up to a temperature T_w ≃ 1400 K, the catalytic properties of the wall increase. For higher temperatures, thermal desorption becomes very efficient and the catalytic properties of the wall decrease. For the typical flow conditions studied, the gas kinetic mechanism has a small influence on the calculated wall heat flux obtained at high pressures, and a higher Influence at decreasing pressures. Besides, the results show that small differences in the calculated wall heat fluxes may correspond to significant discrepancies in the profiles of species concentrations in the boundary layer.