Dsmc simulation of ablating microstructures at flight relevant conditions

The oxidation of carbon-based ablative thermal protection systems is affected by the diffusion of gas from the boundary layer into the mesostructure and the reactivity of the gas with the microstructure (i.e. carbon fibers). To capture both of these effects, a DSMC approach is used and coupled to the ablating FiberGen code. FiberGen allows for movement of the triangles that make up the microstructure to account for gas surface reactions that remove carbon. A Thiele number analysis is performed based on the Stardust reentry trajectory to examine the diffusion of oxygen into the mesostructure at different trajectory points. In order to closely simulate the physics of a hypersonic boundary layer, a procedure for accurately imposing a CFD boundary layer onto a DSMC domain is presented. Subsequently, realistic boundary layer profiles from two Stardust reentry trajectory points are imposed over a mesostructure with and without ablation. This work provides insight on how in-depth oxidation occurs at flight relevant conditions.