Validation of a finite-rate air-carbon ablation model

Abstract

Hypersonic fight produces reactive, high-temperature gas in its 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, like the gas, is often in chemical nonequilibrium and requires a finite-rate ablation 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, but the molecular beam data it is based on was at very low pressure, and therefore the ACA model needs validation at high pressure conditions relevant to hypersonic fight. This thesis provides initial validation by applying the ACA model in a high-fidelity simulation of a recent graphite ablation experiment performed in the von Kármán Institute (VKI) Plasmatron. The ACA simulation results were able to predict the experimentally measured total recession within 0.3 mm (6.7%), the recession rate within 1.4 μm/s (17.7%) and the surface temperature within 151 K (6.6%). The simulation was repeated with an equilibrium-based, state-of-the-practice B' ablation model, the results of which agree with the ACA simulations. This agreement motivates further investigation into the diffusion-limited effects for this flow. A novel ablation Damköhler number is proposed and initially demonstrated for several representative hypersonic conditions.