A Parallelized Oxidation-Driven Surface Recession Framework in DSMC Code, SPARTA

Spacecrafts rely on ablative thermal protection systems (TPS) made of composites consisting of a carbon-based
reinforcement and a polymeric matrix. These materials are designed to withstand high-temperature oxidation and
surface recession during re-entry into the Earth's atmosphere. However, ablation occurs due to a complex interplay of
thermal, mechanical, and chemical factors, making it challenging to determine the individual impact of each on the
TPS's overall degradation. In this study, we have developed an ablation model that can leverage a finite rate carbon
oxidation model to predict material recession and surface states more accurately.
Stochastic PArallel Rarified-gas Time-accurate Analyzer (SPARTA), a direct-simulation Monte Carlo
(DSMC) code, is modified to allow oxidation-driven ablation of implicitly defined carbon surfaces. In SPARTA,
implicit surfaces are generated from the grid corner point values via a marching cubes algorithm, therefore creating a
new set of surface elements every time ablation is performed. The finite-rate oxidation model developed by Gopalan
et. al can perform both gas-surface and pure-surface reactions and is now adapted to tally surface data on a per grid
cell basis. The ablation functionality was also adjusted so once the reactions have occurred, the number of
reactions leading to CO formation can be converted to corner point reduction values; therefore, carbon removal is
directly proportional to surface recession. We also briefly discuss some unique challenges associated with parallelizing
this dynamic surface state and geometry. Finally, we analyze the performance of this parallelized implicit chemistry
model with simple 2D and 3D benchmark cases by producing surface state statistics, area changes over time, and
visualization across a range of surface temperatures and processors with and without load-balancing.