Validation and analysis of a coupled fluid-ablation framework for modeling low-temperature ablator

Ablation of certain highly volatile materials, such as camphor, naphthalene, and dry ice, can be achieved at relatively mild hypersonic conditions in unheated wind tunnels. This provides a convenient way to test fundamental aspects of the ablation process, develop measurement techniques, and validate numerical simulations. In this study, we develop a coupled framework between hypersonic flow and material response solvers and validate the numerical approach against recent experiments conducted by the von Karman Institute of Fluid Dynamics. The flow environment is modeled with an overset near body - Cartesian solver developed within CHAMPS. The solver is equipped with capabilities for automatic mesh generation, adaptive mesh refinement (AMR), and an interpolation algorithm for exchanging boundary conditions with external solvers. The material domain is modeled with a network of one-dimensional rays, incorporating a heat conduction solver, several types of surface ablation models, and a coupled system of surface balance equations required for coupling with the flow solver. The material environment in the simulation aims to closely match the experimental design of the ablating sample, which included a thin layer of camphor applied on top of a copper holder. By taking into account the cooling effect introduced by the back structure, we were able to achieve close agreement with the experimental data for the stagnation point recession and the overall shape change of the geometry. The obtained results are also compared to uncoupled equilibrium-based and steady-state (coupled) solutions, highlighting the importance of the coupled approach for modeling ablation problems. In addition, we explore the effects of different transport properties on the ablation rate of the material, highlighting a strong dependence on the diffusivity of the ablating species. Finally, using the flexibility of the developed algorithm, we explore the effect of the iterative scheme and coupling frequency between the solvers on the accuracy of the solution and the overall duration of the simulation.