Sensitivity Analysis of Radiation in Sub-Orbital Hypersonic Flows

Ionization behind shock waves in sub-orbital hypersonic flows is characterized by thermochemical nonequilibrium processes. Accurate predictions of ionization are required for improved vehicle design, communication blackout mitigation strategies, and radiative heating measures. Incident shock tube experiments that use emission spectra of the flowfield as a diagnostic can be used to infer reaction rates which sensitively influence ionization at key freestream conditions. In the current study, uncertainty in the rate coefficients of chemical processes, vibrational-translational relaxation time scales and energy exchange cross-sections in Park’s two-temperature model of the 11 species air system is used to quantify radiance prediction uncertainty in the vacuum ultraviolet (VUV), visible and near-infrared regimes at freestream conditions of importance to sub-orbital hypersonic flows. Sensitivity analyses of non-equilibrium radiance from specific atomic lines and molecular bands show the importance of NO kinetics in the form of Zel’dovich and NO dissociation reactions.