Sensitivity Analysis of Thermochemical Kinetics Modeling for Hypersonic Air Flows

Abstract

A computational analysis is used to model Mach 5 and Mach 7 flows over a cylinder, where freestream properties are representative of experiments to be conducted in the Hypervelocity Expansion Tube at the California Institute of Technology. A sensitivity analysis is conducted using the polynomial chaos expansion method, and Sobol indices are used to determine which thermochemical nonequilibrium phenomena most affect various quantities of interest. The results show that the dissociation of molecular oxygen through interaction with molecular nitrogen and with atomic oxygen reactions dominates the determination of surface pressure, surface heat transfer, drag, heating rate, and rotational temperature, whereas the first two Zeldovich reactions dominate the surface number density of NO. The reaction is found to be less important than other reactions. Surface pressure and drag are also shown to be relatively insensitive overall. The results also indicate flow separation and recirculation near the trailing edge of the cylinder. These findings may help diagnostic developments to lower discrepancies between computation and experiments, and indicate that the Hypervelocity Expansion Tube experiments should be successful for the future evaluation of thermochemistry modeling.