Detailed simulation of nitrogen dissociation over a sphere

The coupling between a molecule's vibrational state and its dissociation rate is one of, the most important and poorly understood processes in hypersonic flows. The details of this process affect a vehicle's aerodynamics and thermal protection requirements. It also has a direct effect on the level of ionization in the flow field. In this paper, we examine the vibrational relaxation and dissociation process in the forebody region of a 10 cm sphere. We simulate the vibrational exchange mechanisms using the forced-harmonic oscillator and Schwartz-Slawsky-Herzfeld vibrational relaxation models where resonant vibration-vibration exchange is included. A classical impulse' dissociation model simulates the N₂-N₂ and N₂-N dissociation processes. It is found that highly non-Boltzmann vibrational distributions are present along the entire stagnation line which can not be captured by a conventional single-vibrational temperature model. In addition, it is found that mass diffusion significantly effects vibrational distributions and atomic Nitrogen mass fractions.