Multi-Physics Modeling of Ablative Processes

Abstract

As reliability requirements for entry systems become increasingly stringent, the need for predictive modeling of complex configurations grows. Such configurations, like micro-meteoroid and orbital debris (MMOD) impacted thermal protection systems (TPS), often involve highly coupled physics that evolve at disparate length and time scales. This work addresses modeling efforts to characterize thermal response of TPS materials with MMOD impact cavities in high enthalpy flow. The importance of cavity geometric parameters, material properties and multi-dimensionality is quantified with regards to design criteria for system failure. The key findings were that length of conduction path and thermal mass play a significantly more important role in TPS survivability than heating augmentation on the surface due to cavities. It was also shown that 1-dimensional analysis for material response of cavity damaged TPS is highly inaccurate particularly after long exposure times. To enable modeling of complex and highly coupled ablation problems, a multi-physics framework is developed. A methodology for modeling shape change in coupled systems is presented and assessed for validity and performance. The approach taken to model gas-surface interactions and translate coupled surface phenomena to physically meaningful boundary conditions in the distinct solvers is discussed. Particularly, the nature of coupled boundary conditions pertaining to surface energy and mass balance as well as surface chemistry modeling. The developed methodology was used to simulate a shear test in arc-jet conditions in order to assess the validity of the fully coupled approach as well as the implementation of the distinct relevant physical processes. It was found that the current work improves upon the agreement of approaches from literature with experimental results.