Estimations of Rotational Relaxation Parameters in Diatomic Gases

Abstract

The problem of redistribution of translational and rotational energy has been solved for diatomic gases within the framework of the Chapman-Enskog method and the Parker model in the general case of the arbitrary energy exchange ratio. The nonequilibrium gasdynamic equations, transport coefficients and relaxation time have been found for rotational-translational processes in a diatomic gas. The calculations of relaxation time, viscosity, thermal conductivity, and diffusion coefficients are carried out in the temperature range from 200 K to 10,000 K for nitrogen. The calculated parameters and coefficients are compared with the values obtained by the Mason-Monchick approximate method as well as data from experiments in ultrasonic, shock-wave, and vacuum devices. The correlation of the theoretical and experimental data is satisfactory. The applicability of one-and two-temperature relaxation models is discussed. The numerical solutions of the obtained system of the Navier-Stokes equations are analyzed for the cases of nitrogen flow in underexpanded jets and supersonic rarefied gas flow near a sphere.

An ES-BGK model for diatomic gases with correct relaxation rates for internal energies

“…In general, very little information can be found in the literature about the relaxation time of rotation at very low temperatures. However, in Riabov Riabov (2011) one can find a discussion about the discrepancy between the classical consideration of Parker's model and the technique of Lebed and Riabov Lebed & Riabov (1979) for the relaxation times of rotation for T < 100 K. It becomes clear that the Parker model can no longer be used for these low temperatures. Andriès et al Andriès et al (2000) If the vibration modes are neglected, our model reduces to the following translation-rotation ES-BGK model:…”