VV-exchange in direct Monte Carlo simulation of rarefied gas flows

A question of modeling of vibration-vibration (VV) exchange in calculation of rarefied gas flows by the direct simulation Monte Carlo method is considered. Two simple models for VV-exchange in collisions of simple harmonic oscillator molecules are proposed: a model with single-quantum transitions and an extension of the Larsen–Borgnakke model used widely for RT- and VT-exchange. Computation of vibrational relaxation is performed for homogeneous test conditions and for the conditions of an experiment on vibrational population evolution in nitrogen excited vibrationally by a laser. The numerical results obtained are in good agreement with experimental data.