Rotational-translational relaxation effects in diatomic-gas flows

The problem of deriving the nonequilibrium gas dynamic equations from the first principles of the kinetic theory of gases was studied by Ferziger and Kaper [1] in the cases of near-equilibrium and slow-relaxation processes of the energy exchange between internal and translational degrees of molecular freedom. The case of the arbitrary energy exchange ratio was analyzed in [2], [3], [4], [5] for polyatomic gas mixtures. In the present study the problem of redistribution of translational and rotational energy has been solved for diatomic gases within the framework of the Chapman-Enskog method [1], [5], [6] and the Parker model [7] in the general case of the arbitrary energy exchange ratio. The gasdynamic equations, transport coefficients and relaxation time have been found for nonequilibrium processes in diatomic gases [5], [6]. 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 by using the technique of integral brackets [1], [4]. The calculated parameters are compared with the values obtained by the approximate method [8] as well as data from experiments [9], [10] in ultrasonic, shock-wave, and vacuum devices. The correlation of theoretical and experimental data is satisfactory. The applicability of oneand two-temperature relaxation models for para-hydrogen at the rotational temperature range from 0 to 1200 K is discussed. The numerical solutions of the Navier-Stokes equations are analyzed for spherical expanding nitrogen flow and supersonic flow near a sphere.