Simplified Mixing Rules for Calculating Transport Coefficients of High-Temperature Air

Abstract

The transport process of high-temperature air is vital in aerospace fields and has attracted increased attention in recent years. In this paper, an adequate study of factors affecting transport coefficients for high-temperature air is conducted. The results of a different-species model at different pressures and temperatures show that the 9-species air model is applicable to calculate the viscosity and translational thermal conductivity coefficients before significant ionization occurs. Based on the Chapman-Enskog method, simplified mixing rules for calculating viscosity and translational thermal conductivity coefficients of high-temperature air are developed by omitting unimportant matrix elements and assuming the reduced collision integral ratio to a reasonable constant value. The diagonal elements’ magnitude of the transport matrix indicates that collision related to the electrons has a little impact on viscosity but has a great influence on translational thermal conductivity. New simplified mixing rules can accurately calculate the viscosity and translational thermal conductivity coefficients of high-temperature air when dissociation or weak ionization occurs. The improved mixing rules are obviously more accurate than the Wilke mixing rule.