Air-carbon ablation resulting from boundary layer flow over resolved material microstructure

This paper presents ongoing research aimed at predicting the heat flux, shear stress, and reactive species flux on the surface of material microstructure, that comprises modern thermal protection systems for planetary entry missions. While computational fluid dynamics (CFD) simulations provide a great deal of information for thermal protection system design, they do not resolve the meso- and micro-structure of the material. New material structures are under development for various missions and many include carbon fiber structures (porous structures or dense weaves) combined with phenolic resin. The current research presents a methodology of extracting boundary layer flow conditions from a CFD simulation for a specific flight condition and capsule geometry and then imposing this boundary layer flow over resolved meso- and microstructure, using the direct simulation Monte Carlo (DSMC) method. We present new results for the Mars Sample Return mission where both CFD and DSMC simulations include a recent 20-reaction air-carbon ablation (ACA) model. Including gas-surface reactions dramatically changes the composition of the boundary layer, compared to non-reacting surface boundary conditions, as expected. The resulting simulations provide more realistic predictions for the heat flux, shear stress, and reactive species flux experienced by the meso- and micro-structure under flight relevant conditions.