State-Specific Transport Coefficients for Various Vibrational Distributions Taking into Account Varying Molecular Collision Diameter

One of the important issues of modern nonequilibrium gas dynamics is the correct modeling of all possible molecular distributions over internal energy levels, which is necessary for the accurate calculation of physical properties, transport coefficients, and flux terms. In particular, it is of importance for modeling of the thermal protection of re-entry spacecrafts, as well as for hypersonic flight regimes. This study is devoted to the modeling of various non-equilibrium vibrational distributions of molecular species that differ significantly from the well-known Boltzmann and Treanor distributions. The obtained distributions are implemented for the problem of calculation of state-specific transport coefficients, and, in particular, for the calculation of thermal conductivity and shear viscosity coefficients. In addition, the study evaluates the effect of an increasing collision diameter to the transport coefficients calculation. It is shown that the effect of an account for increasing collision diameter is of importance under conditions of strong vibrational non-equilibrium. It is shown that for N2 the contribution of the variable collision diameter to the state-specific thermal conductivity coefficient is significant at temperatures above 8000 K, while for shear viscosity the effect is negligible up to 15 000 K.