Coupled vibration-rotation dissociation model for nitrogen from direct molecular simulations

A new nitrogen dissociation model for direct simulation Monte Carlo (DSMC) is formulated based on reaction cross-sections obtained from quasi-classical-trajectory (QCT) calculations using an ab initio potential energy surface (PES). The proposed model accurately captures the dependence of different molecular energies on the dissociation process, such as favoring due to vibrational and rotational energy. The probability model is then averaged over all molecular energies in the near-equilibrium limit to obtain a dissociation rate coefficient expression, suitable for use in computational fluid dynamics (CFD) calculations. The proposed CFD dissociation model is dependent on average translational, rotational, and vibrational energies and is shown to reproduce nonequilibrium rates, where the average internal energy is not in equilibrium with the average translational energy. An advantage of the proposed models is that they are analytically consistent and therefore could be useful for hybrid DSMC-CFD simulations of hypersonic flows.