Numerical and Experimental Study of the Effects of Surface Temperature and Oxygen Mass Flux on the Ablation of Carbon-Carbon Composites

Abstract

The ablation performance of carbon-carbon composites depends on the environment in which the ablation occurs. At temperatures below 3000 K, the ablation performance of carbon-carbon composites is determined by oxidation, and so it is not sufficient to describe the environment only in terms of surface heat flux, which is the criteria that has typically been adopted for test conditions in ground tests. In this study, the effects of surface temperature and oxygen mass flux on the ablation of carbon-carbon composites were investigated, since they are key factors in the oxidation of carbon-carbon composites. Oxy-kerosene torch experiments were conducted under two surface temperature conditions, of about 1700 K and 2600 K, and with three equivalence ratio conditions. The experimental results were then numerically reconstructed through a coupled analysis of oxy-kerosene torch flow-field modelling, surface thermochemistry, and gas-surface interaction. The effects of surface temperature and oxygen mass flux on the ablation of carbon-carbon composites were analyzed in terms of the mass ablation rate, surface heat flux, and morphology. It was determined that the mass ablation rate is proportional to the increase in oxygen mass flux, even when the surface heat flux and surface temperature were similar. The proportion of heat flux reduction by ablation heat flux was proportional to the increase in oxygen mass flux, and the contribution of oxygen mass flux to the ablation heat flux was enhanced under high surface temperature conditions. Depending on surface temperature and oxygen mass flux, a flat-shape fiber was observed in the morphology analyses, unlike the typical needle-shaped fiber.