A Nonequilibrium Finite-Rate Carbon Ablation Model for Radiating Earth Re-entry Flows

Vehicles entering planetary atmospheres at high speed require an ablative heat shield in order to withstand the high thermal energy flux to the body. The interaction between the ablative products and the flow field is not well characterized. Numerical simulations were conducted to investigate the influence of carbon ablation on shock layer radiation. Data collected from experiments performed in the X-2 expansion tunnel at the University of Queensland was used to compare to the simulations. The model was a short half-cylinder made of isomolded graphite and was tested in 8.6 km/s Earth entry flow. The model surface was heated within a temperature range of 1770-3280 K. The radiation emitted from the CN violet bands was measured by ultraviolet spectrometry in a spectral range from 353-391 nm. This research develops a novel finite-rate surface kinetic model for determining the chemical state of an ablating boundary layer. The proposed ablation model accounts for competing surface reaction processes such as adsorption/desorption, Eley-Rideal mechanisms, oxidation, nitridation, and sublimation. The included oxidation mechanisms predict CO as the primary oxidized product at the considered surface temperatures, which is in agreement with experiment and theory. A previous model had incorrectly predicted CO2 as the primary oxidized product for a majority of the tested surface temperatures. The ablative gas species predicted by this new surface model results in better agreement with experimental spectral measurements than predictions provided by legacy ablation models, and represents a significant improvement in current modeling capabilities for hypersonic nonequilibrium ablating re-entry flows