A Study on the Impact of Mesh Resolution and Diffusion Terms on Thermochemical Non-Equilibrium Flows

Abstract

Numerical simulations of a mixture of oxygen and nitrogen are presented for the Fire II experimental capsule configuration under thermodynamic and chemical non-equilibrium hypersonic conditions. Seven points along the capsule reentry trajectory are considered. Despite the low density of the first point along the trajectory, it is shown that the medium can be modeled as a continuum and that a laminar flow approximation is valid. The finite volume method is used to solve the Navier-Stokes equations, including Park's two-temperature model for chemical dissociation and ionization. A mesh refinement study in the region adjacent to the shock wave is performed based on the Re_cell parameter. Numerical results are compared to experimental data available in terms of convective heat fluxes. Results are presented in terms of thermodynamic and chemical non-equilibrium properties of the gas mixture. Under such conditions, it is possible to observe the occurrence of thermodynamic non-equilibrium through the magnitude difference of the translational-rotational and vibrational-electronic temperature modes inside the shock layer forming upstream of the capsule. Analyses of the thermodynamic and chemical non-equilibrium effects are performed, considering the thermal and viscous diffusion behavior of the flow, and the excitation state of the temperature modes, in addition to the chemical effects of dissociation and ionization of molecules and atoms present in the mixture. Results for each of the seven points on the Fire II capsule reentry path are analyzed and discussed.