Effect of Oxygen Dissociation on Nitric Oxide Ultraviolet Emissions

Abstract

Hypersonic flow over a cylinder was modeled using the direct simulation Monte Carlo method to study how nitric oxide (NO) Ultraviolet emission profiles are a test of high-fidelity thermochemical, nonequilibrium models. For pressures found in typical hypersonic ground facilities, it was shown that the ultraviolet radiation emission profiles are very close to those calculated by assuming Boltzmann equilibrium conditions. Therefore, the NO emission profiles can be tied directly to the ground state NO concentration and flow bulk temperature. Two chemical models differing in the manner in which molecular oxygen is dissociated were considered in this classic canonical-type flow. A comparison of the predicted flowfields with schlieren imagery and surface pressure measurements from previous experiments showed good agreement; however, the sensitivity of these measurements to change in different freestream species concentrations was not found to be strong. Instead, the shapes of the predicted NO integrated emission spatial profiles were observed to be highly sensitive to whether vibrational favoring was considered in the oxygen dissociation model for the same freestream conditions.