Coupled Nonequilibrium Flowfield-Radiative Transfer Calculation Behind a Shock Wave

The coupling between radiation transport and nonequilibrium flow is studied behind a normal air shock wave. A self-consistent electronic specific collisional-radiative model is used to describe the nonequilibrium distribution of N and O populations and a two-temperature model is used to describe the remaining degrees of freedom. The radiation model includes bound-bound, bound-free, and free-free radiative processes. The radiative transfer equation is solved in the one-dimensional planar geometry to provide the radiative source terms involved in the atomic level populations and chemical species conservation equations, and in the energy conservation equations. A line-by-line approach is used to determine the radiative properties. The converged solution is obtained through iterations between the flowfield solver that considers a semi-implicit treatment of the radiative source terms and the radiative transfer solver. Two Earth-entry cases corresponding to trajectory points at high (similar to 76 km) and very high (similar to 91 km) altitudes are simulated. At high altitude, accounting for coupling with radiation leads to small differences on the flow and radiative fields. At very high altitude, radiation significantly depletes the atomic excited levels, and delays ionization and return to equilibrium. Radiation fluxes decrease in both cases.