Direct Simulation Monte Carlo Modeling of Gas Electronic Excitation for Hypersonic Sensing

Numerical procedures based on the direct simulation Monte Carlo method are presented for determination of electronic energy distributions and gas emission in non-ionized hypersonic flows, with intended application to shock-layer emission analysis for a hypersonic remote sensing platform. The proposed modeling approach enables utilization of experimental state-to-state transition rates, and it differs from earlier approaches by greatly reducing the dependence on excited state populations for statistical scatter in computed energy distributions. Calculations are performed for a low-Knudsen-number Mach 10 flow of reacting air around a blunted wedge, and simulation results are employed to compare gas emission with expected signal intensity along a notional signal path. A particularly strong emission contribution from freestream species is found in the region of continuum breakdown around the bow shock, and it is estimated that gas emission should have a very small but potentially nonnegligible influence on si...