Simulation Techniques in Hypersonic Low-density Aerothermodynamics

Hypersonic rarefied flows near a wedge, disk, plate, and sphere were studied under the conditions of wind-tunnel experiments [1-8] and hypersonic flights. The direct simulation MonteCarlo (DSMC) method [9] is used to study the influence of similarity parameters on aerodynamic coefficients in He, Ar, N2, and CO2. It is found that, for conditions approaching the hypersonic stabilization limit, the Reynolds number Re0 and temperature factor tw are primary similarity parameters. The influence of other parameters (specific heat ratio γ, Mach number M∞, and viscosity parameter) becomes significant at Re0 < 10 and values of the hypersonic similarity parameter M∞θ < 1. The numerical results are in a good agreement with experimental data, which were obtained in a vacuum chamber at 0.1 ≤ Re0 ≤ 200. The effect of nonequilibrium processes on flows over blunt bodies is studied by solving the Navier-Stokes equations [10] and the thin-viscous-shock-layer (TVSL) equations [11]. The nonequilibrium, equilibrium and “frozen” flow regimes were examined for various physical processes in air and N2, including rotational relaxation, chemical reactions and ionization. It is found that the binary similitude law is satisfied for blunt bodies in the transitional flow regime. The Reynolds number Re0, in which the viscosity coefficient is calculated by means of stagnation temperature T0, can be considered as the main similarity parameter for modeling hypersonic flows in continuum, transitional and free-molecular regimes [5]. Using Re0, γ, and M∞, it is possible to perform other well-known parameters, such as χ and V for pressure and skin-friction approximations [8]. The Re0 values can be changed by relocation of a probe along the free-jet axis at different distances x from a nozzle exit (Re0 ~ x -2 ). Due to this method [1, 2, 5], fundamental laws of hypersonic streamlining of bodies were discovered and valuable experimental data on aerothermodynamics of various probes was collected [6-8].