Effects of Microstructural Variability on Macroscopic Modeling of Gas-Surface Interaction Study in a Fluid-Material-Structural Coupled Framework

This study develops a coupled multi-physics simulation framework for orthotropic thermal protection systems (TPS) subjected to thermal loading, explicitly incorporating material variability in stiffness and thermal conductivity to evaluate its influence on heat transfer and thermo-mechanical behavior. The framework employs a shared computational grid for solving material response and structural mechanics for KATS, whihc is integrated with the US3D flow solver, enabling comprehensive capturing of temperature-dependent stress, strain, and displacement while accounting for fluid–material response coupling. Results indicate that material variability decreases average temperature penetration but significantly alters the temperature distribution due to fluctuations in thermal conductivity. This non-uniform thermal field induces greater stress variability across the material, thereby increasing directional failure risk beyond that predicted by uniform orthotropic models. The thermal expansion in the material is reduced because of the lower penetration of temperature into the material with the variability. Despite these internal variations, total thermal expansion remains largely governed by geometric constraints and boundary conditions, exhibiting negligible overall change. The analysis excludes effects of pyrolysis, decomposition, porous flow, and charring, which are reserved for future studies. The findings underscore the critical importance of incorporating microstructural variability in macroscopic TPS modeling, as it substantially modifies heat transfer characteristics and stress distributions, with significant implications for accurate failure prediction and robust TPS design under conjugate heat transfer environments.