Modeling of ablation of carbon-carbon composite thermal protection system

This poper is concerned with analytical numerical modeling of ablation behaviour of carbon-carbon (C/C) composites used in the hot spot areas of reentry space and hypersonic vehicles. Of the three modes of ablation (thermal, chemical and mechanical), the chemical (oxidation) is considered to influence the performance of C/C material. The oxidation is divided into two regimes: reaction controlled and diffusion controlled. Which of the two controls the ablation rate depends on the surface temperature. Analytical relations available in the literature are used in the computation of reaction rates, from which surface recession rates are obtained. The oxidation protected C/C materials are considered by using the parameter 'activation energy' in the reaction rate computation. The surface temperatures used in the oxidation rate calculations are obtained from three-dimensional finite element method based nonlinear transient thermal modeling. The variations of ambient temperature, pressure and oxygen concentration with altitude are taken into consideration to model the reentry condition. This is a moving boundary problem. As the recession takes place, newer surfaces are exposed to aerodynamic heating. Numerical examples are presented to show the effect of: heat flux, altitude and oxidation protection.