Analysis of mass diffusion theory and models for high-temperature multi-component gases

Abstract

The correct knowledge of physical theory and models of the mass diffusion for high-temperature multi-component gas flows is of importance for accurately simulating the aerothermodynamic properties of hypersonic vehicles. Mass diffusion mechanism from the phenomenological theory (the Fick’s and the modified Fick’s model) and the kinetic theory (the self-consistent effective binary diffusion model and the Stefan-Maxwell model) is theoretically analyzed to explore the reasons for model differences in application to CFD simulations of Earth reentry flows. Theoretical analysis shows that the other three models rather than the Fick’s model ensure the self-consistent condition. A difference term Ai is proposed to represent the discrepancy of the self-consistent effective binary diffusion model and the modified Fick’s model. Numerical results indicate that whether the mass diffusion model satisfying the self-consistent condition has great influence on surface heat transfer, with the maximum difference up to 18% under the fully-catalytic wall. The aerothermodynamic properties obtained by the modified Fick’s model and the self-consistent effective binary diffusion model are in good agreement, which can be explained by the small Ai values. It is proved that theoretical derivations and numerical results are consistent to conclude that the modified Fick’s model and the self-consistent effective binary diffusion model of rigorous physical fundamental are suitable to describe the mass diffusion process of high-temperature multi-component gases.