NONEQUILIBRIUM THERMAL-RADIATION FROM AIR SHOCK LAYERS MODELED WITH DIRECT SIMULATION MONTE-CARLO

At re-entry velocities it is generally agreed that the radiation associated with transitions between excited electronic states of atoms and molecules is responsible for the bulk of the thermal radiation emitted from the shock wave area. This article deals with the evaluation of thermal radiation emitted from hypersonic shock waves in real air using the direct simulation Monte Carlo method. The calculation of electronic excitation is made without assuming equilibrium for the distribution of the energy states, and measured or theoretically evaluated cross sections are used to determine the electronic excitation of atoms and molecules in the flow and the subsequent thermal radiation. The results with this new scheme are compared with available experimental data and existing numerical methods. The test cases are based on an AVCO Everett shock-tube experiment and on the axisymmetric flowfield of a blunted Mars-net re-entry vehicle. The method is in good agreement with both experimental data and results given by other methods. Discrepancies are evaluated and discussed.