Design and evaluation of variable porosity charring composite for thermal protection system of reentry vehicles

Charring composites can provide the most efficient thermal protection shield for the thermal protection system (TPS), which is essential for hypersonic reentry vehicles. It is of great importance to clarify the implication of different porosity configurations of charring composite on the bondline temperature. In the present study, a one-dimensional transient thermal model considering the pyrolysis without the surface recession is built and validated. Based on this model, the thermal protection performance of various porosity distribution design schemes is analyzed when keeping the total pore volume unchanged. The present results show that the scheme with the linear increasing porosity from the bondline to the heated surface can decrease the bondline temperature by 7.8 K and 15.8 K compared with the homogeneous scheme and the linear decreasing scheme, respectively. Further, a scheme with parabolic increasing distribution of porosity are evaluated. It is found that it can reduce the bondline temperature by an additional 2.9 K.