A chemical equilibrium method for hypersonic flow simulations

Abstract

In this paper, we report a new and efficient method to simulate high-speed, chemically reacting flows with a chemical equilibrium model. This computational method is based on the Helmholtz free-energy minimization with two additional treatments to enhance computational efficiency. First, an estimation scheme for species compositions is implemented to either bypass the numerical iterations or significantly reduce them in the free-energy minimization procedure. Second, a frozen flow calculation method is adopted to take advantage of the non-reacting part of the hypersonic flow field. In general, 95% of the full minimization procedure is avoided by using the two methods and no accuracy is sacrificed in the final converged solution. In addition, the flow solver adopted in the present study is incorporated with comprehensive, high temperature, gas property models to simulate hypersonic flows and employs an implicit, finite-volume, lower-upper (LU), time marching scheme to solve flow equations in a fully coupled and very efficient manner. Finally, hypersonic internal flows under serve conditions are simulated as numerical examples. The results are compared with those of a finite-rate model, in which 11 species equations coupled with flow equations are solved simultaneously. The results clearly depict differences in the flow characteristics predicted by the two chemistry models.