Development of a Nonequilibrium Finite-Rate Ablation Model for Radiating Earth Reentry Flows

Abstract

Thermal protection system design for atmospheric reentry vehicles remains a challenging and complex problem. Recent advances in computational modeling of air–carbon interactions consider competing finite-rate reactions on a limited number of available surface sites. One of the most advanced kinetic models is due to Zhluktov and Abe. However, the Zhluktov and Abe model only describes the oxidation and sublimation of carbon and has no nitridation mechanism. The following study develops several modifications to the Zhluktov and Abe air–carbon model that account for all three reaction mechanisms with the goal of improving cyanogen shock-layer radiation predictions to recent experimental results. First, the study examines two possible paths for carbon nitridation and then assesses the augmented surface reaction model in a representative blunt-body reentry flow. Second, a sensitivity analysis is performed to determine which surface reactions have the most impact on altering cyanogen radiance predictions. It was found that modifications to the oxidation mechanisms significantly improved the comparisons and the nitridation mechanism had a minor effect. Specifically, it was determined that carbon monoxide must be the principal oxidation product at high surface temperatures instead of carbon dioxide, as the Zhluktov and Abe model had originally predicted. More detailed measurements of both the carbon oxidation and nitridation reactions at higher surface temperatures are required to further validate and improve the rate parameters derived in this study.