Modeling of Thermal Dissociation in Nonequilibrium Hypersonic Flows

Numerical simulations are presented of steady state, hypersonic blunt body nitrogen flow for conditions under which there is considerable thermal dissociation. The internal energy relaxation processes of vibrational energy transfer, dissociation and recombination were treated using state-to-state kinetics of diatomic nitrogen. The state-specific rates were incorporated into a solution of the master kinetic equations coupled to the fluid dynamic equations to describe the thermo-chemical nonequilibrium phenomenon in high temperature hypersonic flowfields. Results of the detailed flowfield simulations were compared with Park model and depletion model. The state-specific dissociation and recombination rates were employed in the study of vibrational bias and depletion effects. Vibrational bias was strong for both the dissociation process and the recombination process at temperatures ranging from 6,000 to 20,000 K. The shock-standoff distance of the full state-kinetic implementation and the depletion model were consistent with each other and resulted in a greater shock-standoff distance compared with the Park model for a Mach 19 nitrogen flow past a hemisphere cylinder of radius 0.1524 m.