Gas-surface interaction phenomena have a strong impact on the heat flux experienced by atmospheric entry bodies in the hypersonic regime. Numerically, they can be expressed as a boundary condition to be imposed to the Navier-Stokes equations to achieve predictive engineering simulations. The mass and energy conservation can be abstracted in a thin layer containing both the solid and the gas phases. Such a balance was implemented in the open source MUTATION++ library. It is convenient to easily plug verified models in any type of CFD solver to model the response of material surfaces. We have extended the library to accommodate a state-of-the-art nitridation and nitrogen recombination mechanisms derived from beam experiments. MUTATION++ was coupled to US3D, a high-fidelity finite-volume flow solver, to simulate an experimental campaign conducted in the VKI Plasmatron facility. The experiment consists in applying a subsonic high-enthalpy nitrogen flow over an axi-symmetric ablative material sample. The simulation results on the stagnation line were compared to those obtained using a one-dimensional solver. Both results showed good agreement, verifying the implementation of the boundary condition. The computational model predicts a lower mass blowing rate than the experimental value. The catalytic behaviour of the mechanism, in agreement with the beam experiment predictions, induces higher heat flux values than those expected for the testing conditions of the Plasmatron facility.

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The effect of finite-rate internal energy transfer on shock interaction mechanisms of CO 2dominated flows is investigated. The polyatomic molecule has a relatively low characteristic vibrational temperature that causes vibrational degrees of freedom to be excited across a shock wave at hypersonic regimes. In this paper, the impact of accounting for the time associated to the relaxation of this process, as opposed to assuming instant thermal equilibrium, on the shock structures occurring in the flowfield over a double-wedge geometry is numerically studied. A Mach 9 flow over two different geometries is simulated with two different models, the two-temperature model of Park and the thermally perfect gas model. Simulations are carried out with the SU2 software that is coupled to the Mutation++ library, providing thermodynamic, chemical kinetic and transport properties of any mixture of gases for a given state of the flow. Anisotropic mesh adaption is used with the AMG library to accurately capture highly directional and high-gradient localized flow features. Results show that different ways of modelling the effect of vibrational relaxation have a major impact on the size of the compression corner separation bubble, leading to different shock wave systems in this region. As a consequence, the obtained shock interaction mechanisms differ as well. The shock patterns obtained for the thermally perfect gas model result in stronger impingement on the surface and higher aerodynamic loads of pressure and heat flux.

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