Feasibility of Non-Equilibrium Hypersonic Flow Measurements at the Small Particle Hypervelocity Impact Range

Currently used hypersonic flow models, such as high-enthalpy reaction and energy relaxation rates, are based on experiments conducted at relatively low flow enthalpies and are highly uncertain. This paper presents analysis of the feasibility of calibrating hypersonic flow parameters using free-flight experiments at the Small Particle Hypervelocity Range (SPHIR) at Caltech/JPL. Chemically reacting, nonequilibrium flows around a 2-mm diameter spherical projectile are modeled using the Direct Simulation Monte Carlo (DSMC) method. The flowfields generated by DSMC simulations are used to calculate emission spectra in order to determine the observable radiation in UV/vis spectral range. Bayesian calibration and generalized polynomial chaos expansion (gPCE) techniques are used to assess the sensitivity of observable flow properties to key reaction rates. These techniques are then used to predict how experimental resolution would affect the uncertainty in the calibrated parameters.