Role of State-to-State Kinetics in Determining Transport Coefficients for Hypersonic Flow Simulations

Abstract

A numerical study is performed to assess the influence of thermochemical nonequilibrium on the transport coefficients used in Computational Fluid Dynamics (CFD) simulations of hypersonic external flowfields. An quantitative assessment is made of transport coefficients from simplified methods of Blottner curve fits and Variable Hard Sphere (VHS) model on the numerical solution of a Mach 23 flow past a sphere cone, the RAMC-II test case. The equations derived by Kustova [1] in the state kinetic approach for calculating transport coefficients from the Chapman-Enskog solution of the Wang-Chang Uhlenbeck equation were used to conduct a parametric study for assessment of the effect of the following parameters on the state-specific diffusion coefficients: (1) Widely different population distributions, (2) Atomic mass concentration, and (3) Binary atomic to molecular diffusion coefficient ratio. The present study is a first step to quantify the relative importance of the parameters considered for a future implementation of the computationally expensive state-kinetic transport coefficients in multi-dimensional fluid dynamic flow solvers for flow conditions where the more general state kinetic approach becomes necessary.