ANALYSIS OF DSMC REACTION MODELS FOR HIGH TEMPERATURE GAS SIMULATION 1)

The non-equilibrium phenomenon of thermochemical coupling has been a difficult problem in high temperature aerothermal dynamics, and hinders to analyze phenomena such as cell structure of detonation wave and ignition speed of low temperature combustion. In this paper, typical chemical reaction models (TCE, VFD, QK models) employed in the direct simulation Monte Carlo (DSMC) simulation are analyzed using two examples (namely, N${\mathrm{}}_{{\mathrm{}}_2}$ dissociation at high temperature, and chain displacement reaction in H${\mathrm{}}_{{\mathrm{}}_2}$? O${\mathrm{}}_{{\mathrm{}}_2}$ combustion) from microscopic reaction probability, vibrational state specific reaction rates, total reaction rate under thermal nonequilibrium condition, and post-collision redistribution of internal energy. It is found that the probability distribution of vibrational energy of reacted molecules deviates from the equilibrium Boltzmann distribution for both the high temperature dissociation reaction having high activation energy and the chain displacement reaction having low activation energy. The VFD model with strong vibrational favored contribution can predict well the high temperature dissociation reaction, whereas the TCE model (a special case of VFD model) and QK model are better for the chain displacement reaction. Besides, the post-collision redistribution of internal energy should follow the principle of detailed balance, as small deviations may cause inequality between the translational and vibrational energy under final equilibrium state. The DSMC simulation results also show that the vibrational favor of chemical reactions has an obvious effect on the thermochemical coupling process. Particularly, because molecules having high vibrational energy are more easily to have chemical reactions, the decrease of the average vibrational energy of the gas will affect the subsequent chemical reactions.