Thermal analysis of hypersonic flows of carbon dioxide and air in thermodynamic non-equilibrium

•Numerical simulations of carbon dioxide and air flows are presented for hypersonic conditions.•The spatial distribution of different nondimensional parameters relevant for the flow and thermal analysis is presented for carbon dioxide and air flows.•Different shock wave topologies and species dissociation profiles lead to changes with respect to thermal non-equilibrium although freestream conditions are relatively similar for carbon dioxide and air.•A grid refinement study shows that the calculation of surface heat flux is very dependent on the first cell wall-normal distance.•The accurate capture of ionization effects is shown to have an important role in the thermodynamic non-equilibrium for more extreme Mach number flows. Numerical simulations of carbon dioxide and air flows are presented for the Mars Pathfinder experimental capsule configuration under hypersonic conditions. Despite the low density flows, 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. Results are presented in terms of heat flux distributions over the capsule surface and good agreement is observed between simulations and experimental data. Although freestream conditions are relatively similar for both gas mixtures, the different shock wave topologies and species dissociation profiles lead to changes with respect to thermal non-equilibrium, presented in terms of the translational-rotational and vibrational-electronic temperature modes. Ionization effects are also investigated for an air flow at more extreme conditions, with an even lower freestream density and higher Mach number. An assessment of chemical species models shows that ionization of free nitrogen and oxygen atoms in the air mixture must be accurately captured since it causes large variations in the thermal non-equilibrium process, substantially altering the surface heat flux.