A Study of Ablation-Flowfield Coupling Relevant to the Orion Heatshield

The coupled interaction between an ablating surface and the surrounding aerothermal environment is studied. An equilibrium ablation model is coupled to the LAURA flowfield solver, which allows the char ablation rate ṁ c to be computed as part of the flowfield solution. The wall temperature T w and pyrolysis ablation rate ṁ g may be specified by the user, obtained from the steady-state ablation approximation, or computed from a material response code. A 32-species thermochemical nonequilibrium flowfield model is applied, which permits the treatment of C, H, O, N, and Si-containing species. Coupled ablation cases relevant to NASA's Orion multipurpose crew vehicle heat shield are studied. These consist of diffusion-limited oxidation cases with Avcoat as the ablation material. The ṁ g values predicted from the developed coupled ablation analysis were compared with those obtained from a typical uncoupled ablation analysis. The coupled results were found to be as much as 50% greater than the uncoupled values in regions of turbulence. This is shown to be a result of the cumulative effect of the two fundamental approximations inherent in the uncoupled analysis.

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