Numerical simulation of aerothermal flows through ablative thermal protection systems

The interaction between a chemically reactive boundary layer and an ablative material is one of the most difficult challenges for the accurate prediction of the heat fluxes during atmospheric entries of spacecraft. New physico-chemical models and computational methods need to be developed to understand the material response of a new class of light carbon composite ablators in a hypersonic flow. This work proposes the development of a unified tool that solves both the material and the flow inside a single computational domain thus capturing the interactions between the flow and ablated geometry. This continuum description is flexible enough that it can go smoothly from a plain fluid region to a receding porous medium. The tool implementation is based on a high order discontinuous Galerkin discretization and it is verified against several test cases of increasing physical complexity. It takes into account the volume ablation phenomenon in the highly diffusive regime, which is usually neglected. Existing models for the description of carbon fibers oxidation are discussed. The numerical results in this work suggest that more accurate models accounting for microscale information should be developed in order to predict the recession accurately. Finally, we describe two other approaches implemented to treat ablation problems. We present first a material response code and then its loose coupling with a CFD code. These tools are validated but do not capture the volume ablation phenomenon. This work constitutes one of the first strongly coupled approaches for the high-fidelity analysis of the aerothermal performances of low-density ablative materials.