Permeability of porous microstructure in thermal protection system under high-temperature reactive gas conditions

The transport properties of thermal protection materials are fundamentally altered by high-temperature chemical reactions during hypersonic entry, which is crucial for accurately predicting material response and thermal protection performance. This study employs the direct simulation Monte Carlo (DSMC) method to investigate the permeability characteristics of typical thermal protection material porous microstructures under high-temperature reactive gas conditions. Using a 3D needle-punched carbon preforms as the porous microstructure sample, the influence of flow parameters (gas temperature and composition) and thermochemical effects (internal energy excitation and chemical reactions) on the material permeability is examined across three temperature levels (1000, 1600, and 2850 K) and three gas compositions (pure O2, half O2/half O, and pure O). Non-reactive mixtures exhibit linear permeability-pressure relationships which follow the Klinkenberg model. However, chemical reactions significantly induce nonlinear variations, especially at higher temperatures and O concentrations. Complex flow patterns, including non-uniform mass flux distributions and localized flow reversals, are observed in reactive cases. The results reveal that the interplay between chemical reactions, diffusion, and flow dynamics significantly influences permeability characteristics.