二原子分子振動遷移衝突モデルの構築 : 第1報,振動遷移確率(流体工学,流体機械)  [in Japanese] Modeling of a Vibrational Transition Collisional Model for Diatomic Molecules : 1st Report, Vibrational Transition Probability(Fluids Engineering)  [in Japanese]

The direct simulation Monte Carlo (DSMC) method is widely used for simulating rarefied gas flows, and in most cases, the phenomenological model with a local equilibrium assumption is chosen as a collision model. Since most collisions in the rarefied gas regime are binary ones, to make the vibrational transitional collision model for the DSMC method without the local equilibrium assumption, binary collision processes of diatomic molecules were analyzed. The semiclassical approach, in which the vibrational motion is treated quantum mechanically and other degrees of freedom are investigated with the classical mechanics, was introduced. The scheme was verified using the vibrational transition rate coefficient comparing with the empirical relation and the existent numerical results. The transition probability was obtained as a function of the initial translational and rotational energy. From collinear collisions, the transition probability can be described with a simple function of the relative translational energy. The total rotational energy of collisional pairs is appeared to be important for general collisions with rotational energies.