Ablation: Modelling and Evaluation Experiments

Abstract

High heat flux is encountered in space applications in re-entry flight at the thermal protection system, especially at sharp leading edges such as engine intakes, and in combustion chamber liners. Therefore, apart from the passive, radiatively cooled heat shield of C/C-SiC, active cooling systems are of special interest for the use in severe thermal environments where the passive systems are inadequate. Active cooling includes film cooling with slit, showerhead, effusion, and transpiration configuration, the latter of which will be discussed here. Another approach to thermal protection is the ablative heat shield in which the material transfers the energy into chemical degradation. It is used for high speed and high enthalpy re-entries. The degradation process is a complex combination of physical processes and chemical reactions such as evaporation of moisture, swelling, and pyrolysis within the material and recession due to oxidation and nitridation at the material surface and within pores. The material thermal response is governed by heat transfer to and within the component, the reaction kinetics and blowing of the pyrolysis gases. The contribution presents the analysis of heat transfer between coolant and structure in transpiration cooling and wall temperature response for both, chemically transforming ablation- and transpiration-cooled re-entry thermal protection systems and compares calculatory results to measurement data.