Validation of a nonequilibrium air chemistry model in MACH2 and applications to weakly-ionized hypersonic flow

The effects of non-equilibrium air chemistry have been incorporated into the time-dependent, 2 1/2 dimensional, axisymmetric, magnetohydrodynamics solver MACH2 utilizing the well-established reaction model presented by Park. The two-temperature model accounts for the effects of finite-rate chemical reactions among 11 species (N₂, N, O₂, O, NO, N₂ ⁺, N⁺, O₂ ⁺, O⁺, NO ⁺, and e^-), vibrational relaxation according to the empirical method of Millikan and White, and preferential dissociation of molecules with higher vibrational energy. The predicted MACH2 flowfields show good agreement to the experimentally deduced shock stand-off distance of nitrogen flow over spheres in a wind tunnel, the shock stand-off distance of spheres fired into air in a ballistic test facility, and the electron number density on the surface of the Ram-C re-entry experiment. Simulations of a magnetic dipole located in a blunt-nosed cone show the expected dependence of the shock-stand off distance on the magnitude of the magnetic field, demonstrating applicability of the upgraded MACH2 code to problems involving the interaction of electromagnetic fields with a weakly-ionized gas.