Dissociation Modeling in Hypersonic Flows Using State-to-State Kinetics

Abstract

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 and dissociation were treated using state-to-state kinetics of diatomic nitrogen. To gain understanding of the role of vibrational―translational rates on dissociation, the vibrational―translational rates were implemented in a ladder-climbing model, and the effect of vibrational bias on dissociation was investigated. For temperatures up to 25,000 K, a simplified depletion model with two different sets of vibrational―translational rates established the sensitivity of depletion to the relative magnitude of vibrational―translational and dissociation rates for dissociation in nitrogen. State-specific vibrational―translational and dissociation rates were incorporated into a solution of the master kinetic equations and coupled to the fluid dynamic equations to describe the thermochemical nonequilibrium phenomenon in high-temperature hypersonic flowfields. The flowfield consists of a Mach 19.83 nitrogen flow past a hemisphere cylinder with a radius of 0.1524 m. The full state-specific dissociation model, consisting of 48 quantum levels in the vibrational manifold, was coupled to the fluid dynamic equations. For temperatures in the shock layer ranging from 9000 to 21,000 K, the dissociation primarily takes place from the lower energy levels.