Finite-Rate Modeling of Air–Carbon Ablation in a Plasma Wind Tunnel

Hypersonic flight produces reactive high-temperature gas in the shock layer, often in a state of thermochemical nonequilibrium. This gas can react with the vehicle’s surface and remove significant amounts of material, known as chemical ablation. The gas–surface interface is often in chemical nonequilibrium and may require a finite-rate surface-chemistry model to accurately characterize ablation. Recently, a new finite-rate air–carbon ablation (ACA) model for hypersonics was introduced based on molecular beam experimental data. The model captures temperature and pressure dependence of the surface reactions. However, it is based on low-pressure molecular beam data, and therefore it needs to be evaluated at high-pressure conditions relevant to hypersonic flight. This work exercises the ACA model in a high-fidelity simulation of a recent graphite ablation experiment performed in a Plasmatron facility at the von Kármán Institute. At the stagnation point, the simulation predicts the experimental total recession within 0.3 mm (6.7%), the recession rate within 1.4 μm∕s (17.7%), and the surface temperature 150 K (6.6%) lower. In addition, results away from the stagnation point are compared to the experiment, demonstrating comparable surface trends. The simulation is repeated with an equilibrium-based state-of-the-practice B⁰ ablation model, the results of which agree with the ACA simulations. These results provide an encouraging first step in proving the high-pressure validity of the model’s predictions; however, additional comparisons will be needed to fully validate the ACA model, particularly in the reaction-limited regime.