Vibrational non-Boltzmann effects on the dissociation rate of oxygen

Abstract

Both the internal energy nonequilibrium and the NB effects of the vibrational state distribution influence the calculation of the dissociation rate coefficient. The state-to-state (STS) method gives the exact dissociation rate coefficients under the influence of two nonequilibrium effects, while the single group linear maximum-entropy (SGLM) model only considers the internal energy nonequilibrium effects. Therefore, the ratio ζ of the dissociation rate coefficient calculated by the STS method and the SGLM model is used in this paper to describe the NB effects on the dissociation rate coefficient. The zero-dimensional (0D) heating adiabatic thermochemical nonequilibrium process of oxygen was simulated by the STS method with a post-surge temperature of 7000–11 000 K. The variation regularity of the NB effects in the relaxation process were investigated using ζ, and it was found that the NB effects were mainly affected by temperature. And then the relaxation process after the normal shock with the same post-surge temperature of 7000–11 000 K was simulated. The NB effects in the two non-equilibrium processes were compared, and it was found that although there is a conversion between internal energy and fluid kinetic energy in the latter, the NB effects in both processes have similar change rules with similar temperature change rules. If the specific internal energy is the same, the NB effects in both processes are also quantitatively consistent. This finding provides a basis for the improvement of the nonequilibrium model considering the NB effects.