A Prediction Technique for Ablative Material Performance under High-Shear Re-Entry Conditions
Ablation tests of cones and wedges in high-performance hyperthermal test facilities have led to the development of an analytical technique for the prediction of heat shield material response to combinations of shear and heat flux higher than can be simulated. Exposure of composite materials to a high heat-transfer environment results in the development of a relatively weak char layer which is susceptible to removal by aerodynamic forces. Knowledge of the rate of char formation as obtained from thermochemical calculations is used in conjunction with the test recession rates to determine the maximum sustainable depth of char at any test shear level. This depth is shown to be constant for higher heat fluxes and to vary inversely with the total surface shear for higher shear levels. Internal temperature profiles and pressure gradients are considered, and the analysis is extended to materials forming liquid layers.