Nonequilibrium and Rarefaction Effects in the Hypersonic Multicomponent Viscous Shock Layers

The effects of rarefaction and nonequilibrium processes on hypersonic rarefied-gas flows over blunt bodies have been studied by the Direct Simulation Monte-Carlo technique (DSMC) and by solving the full Navier-Stokes equations and the equations of a thin viscous shock layer (TVSL) under the conditions of wind-tunnel experiments and hypersonic-vehicle flights at altitudes from 60 to 110 km. The nonequilibrium, equilibrium and “frozen” flow regimes have been examined for various physical and chemical processes in air, including excitation of translational, rotational and vibrational degrees of molecular freedom, as well as dissociation, chemical reactions, and ionization in the layers near catalytic body surface. The influence of similarity parameters (Reynolds number, temperature factor, catalyticity parameters, and geometrical factors) on the flow structure near the blunt body and on its aerodynamic coefficients in hypersonic streams of dissociating air is studied. The analysis of the catalytically influenced zone of the flow near the surface demonstrates that in order to increase the accuracy of the determination of heat flux values, it is necessary to utilize more reliable information on transfer properties of multicomponent gas mixture and the constants of chemical reaction rates. The main characteristics of the catalytically influenced zone (its width, temperature, and concentrations of species on the external boundary of the zone) can be useful for development of new approximation methods of predicting the heat fluxes at catalytic surface materials of a vehicle. The numerical results are in a good agreement with experimental data, which were obtained in wind tunnels at low and moderate Reynolds numbers from 1.49 to 5130, as well as STS flight data. It has been confirmed that the binaryscaling similitude law is satisfied for blunt bodies in the transition flow regime.