Two-way coupled simulations of stagnation-point ablation with transient material response

Abstract

Ablative materials are extensively used in aerospace applications to protect the integrity of the spacecraft during atmospheric entry. Both thermal and mechanical stresses have to be withstood in the severe operating conditions typical of space missions. An accurate modeling of the phenomena taking place when these materials are exposed to such a harsh environment is crucial to ensure the success of future, more demanding, missions. This study aims to couple two tools able to handle two different aspects of the ablative material modeling: a stagnation-line flow solver featuring an integrated ablative boundary condition, and a material response code. The coupling algorithm allows for time accurate solutions of the ablative material thermal response accounting for detailed surface chemistry, in-depth material behavior, and surface recession. Two different coupling strategies have been implemented, based either on a direct or an iterative procedure. The developed tool is used to rebuild plasma wind tunnel experiments performed in the von Karman Institute Plasmatron facility. The outcomes of the two strategies are compared, showing a satisfactory agreement with the experimental data. Among the two analyzed coupling procedures, the direct coupling proved to be computationally less expensive, while conserving the same accuracy of the more complex iterative procedure for the analyzed cases. A sensitivity analysis is also conducted to understand the discrepancy with experimental data and show the effects of four uncertain material parameters: thermal conductivity, density, emissivity, and catalytic efficiency.