High-Fidelity Modeling of Ablation and Coupled CFD-Material Response

The goal of the research funded under the fellowship award has been to advance the state-of-the-art in the modeling of ablative spacecraft thermal protection systems. Historically, models have generally been of the volume averaged variety, and the various closures found within them have involved a great deal of empiricism, as well as simplifying assumptions which likely neglect important physics (e.g. non-equilibrium chemistry, etc.). Broadly, the approach taken to improve upon this was to study the physics of ablation at the microscale. An illustration of this multiscale spproach can be seen in Fig. 1. The schematic seen in the top left represents the scale and level of detail employed in the legacy material modeling tools used in NASA, and the broader community for the last 40 years. The image in the top right shows a simuation performed with the capability developed under this research. Here we are simulating all of the relevant physics down to the scale of the individual fibers in the material. It has only been recently that advances in numerical and computational capabilities have allowed for such detailed simulations of these complex materials and properties, and this research has attempted to leverage that. In order to do this we implemented several novel new techniques within the framework of the Direct Simulation Monte Carlo (DSMC) method. The DSMC method allows for much greater amount of physics to be simulated than had been done in previous work. For example, it can simulate the convection of gas through the microstructure, as well as chemical reactions in the flow. Furthermore, it allows for more physics based implementations of gas-surface interaction models critical to the simulation of thermochemical ablation. The investigations performed under this research grant have shown that this approach is indeed feasible, and more than that, can provide both practical information for engineering models, as well as physical insight into the important phenomena in this complex process which may inform future high-fidelity models. There is now tremendous interest within the ablation modeling community – including NASA, as well as academia – in developing this or similar methodologies further, and applying it/them to new problems