Effects of thermochemical non-equilibrium in the boundary layer of an ablative thermal protection system: A state-to-state approach

In the era of space exploration, one of the fundamental goals is the investigation of the atmospheric re-entry of a space vehicle, which undergoes tremendous heat load due to the shock waves forming in front of its thermal shield. In the view of heat mitigation, ablative materials are employed for the design of the Thermal Protection System (TPS) of most of the modern vehicles. Such materials essentially modify the nature of the gas in the boundary layer due to the interaction of the solid and gas phases. Thanks to the material consumption, heat load is mitigated at the expense of ablated species which significantly contaminate the boundary layer gas mixture. In this context, this work aims at characterizing the aerothermodynamics environment around a bluff body in the presence of ablation and thermochemical non-equilibrium. Specifically, a five species neutral air mixture (N2, O2, NO, N, O) is combined with a six ablated species mixture (CO, CN, CO2, C, C2, C3). Two test cases are considered. Firstly, a subsonic pure nitrogen flow past an ablative sample is simulated, which is used as verification study by direct comparison with numerical results. For this reason, a classic multitemperature (mT) approach is employed to handle non-equilibrium. The second test case is a well-known hypersonic air flow past a spherical body used as a benchmark to assess the influence of ablation. In this case, two different kinetics models are used, namely the classical multitemperature and the more sophisticated State-to-State (StS) approach.