Nonequilibrium flow through porous thermal protection materials, Part I: Numerical methods

Numerical methods are developed to simulate high temperature gas flow and coupled surface reactions, relevant to porous thermal protection systems used by hypersonic vehicles. Due to the non-continuum nature of these flows, the direct simulation Monte Carlo (DSMC) method is used, and the computational complexity of the simulations presents a number of unique challenges. Strategies for parallel partitioning, interprocessor communication, complex microstructure geometry representation, cutcell procedures, and parallel file input/output are presented and tested. Algorithms and data structures are developed for a microstructure generation tool called FiberGen that enables realistic microstructures to be constructed based on targeted fiber radius, orientation, and overall porosity, with user defined variations about these values. The data structures and algorithms associated with FiberGen are robust and efficient enough to enable DSMC simulations where the microstructure geometry changes to directly simulate ablation problems. Subsonic boundary conditions are described and validated, and a number of example solutions are presented. The example problems demonstrate the difference between surface ablation and in-depth volume ablation regimes for porous TPS materials.