Vibrational-translational energy exchange models for the direct simulationMonte Carlo method

The model which controls the distribution of energy among the different mol ecular modes is a crucial component of accurate simulation of nonequilibriu m rarefied flows. Two new models for the direct simulation Monte Carlo meth od that govern energy redistribution between the translational and vibratio nal modes are presented here. The first model is a modified form of the phe nomenological Borgnakke-Larsen model. The probability of inelastic collisio n is evaluated using the relative velocity of collision. The second energy exchange model considered in this study is the multiple quantum-step transi tion model. The process of vibrational relaxation occurs through transition s between the different energy levels, allowing jumps of more than one leve l. Probabilities of activation and deactivation which depend on the relativ e velocity are used here. The new models are compared with existing schemes for several conditions. Significant differences are found for the vibratio nal energy distribution function computed in a hypersonic bow-shock wave. ( C) 1999 American Institute of Physics. [S1070-6631(99)02408-3].