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We propose to couple a state-resolved rovibrational coarse-grain model to astochastic particle method for simulating internal energy excitation anddissociation of a molecular gas. An existing coarse-grain model based on theNASA Ames ab initio database for the N2-N system is modified usingvariably-spaced energy bins. Thermodynamic properties of the new coarse-grainedmodel closely match those of the full set of rovibrational levels over a widetemperature range, using a number of bins much smaller than the completemechanism. The chemical-kinetic behavior of the original equally -- and newvariably -- spaced bin formulations is compared by simulating excitation anddissociation of N2 in an adiabatic, isochoric reactor. The variably-spacedformulation is better suited for reproducing the dynamics of the full databaseat conditions of interest in Earth reentry. Furthermore, we discuss details ofour Direct Simulation Monte Carlo (DSMC) implementation for the coarse-grainmodel and describe changes to the collision algorithm necessary to accommodateour state-resolved reaction mechanism. The DSMC code is then verified againstequivalent master equation (ME) calculations. In these simulations,state-resolved cross sections are used in analytical form. They verifymicro-reversibility for the bins and allow for faster execution of the code. Inour verification, we obtain very close agreement for the N and N2concentrations, as well as the translational and rovibrational modetemperatures obtained independently using both methods. In addition tomacroscopic moments, we compare internal energy populations predicted atselected time steps via DSMC and ME. We observe good agreement between bothmethods within the statistical scatter limits imposed by DSMC. In future work,the rovibrational coarse-grain model coupled to the particle method will allowus to study 3D reentry flow configurations.

journal of chemical physics online/the journal of chemical physics/journal of chemical physics

Coupling of state-resolved rovibrational coarse-grain model for nitrogen  to stochastic particle method for simulating internal energy excitation and  dissociation