A Gas-Surface Interaction Model for the Numerical Study of High Temperature Flows Over Pyrolyzing Ablative Materials

In the present study, modified surface mass and energy balances have been implemented in the ablative boundary condition of a two-dimensional full Navier-Stokes solver, to take into account the pyrolysis gas injection. A finite-rate ablation model is used, with steady-state ablation approximation to obtain the surface temperature. Hence, with this approximation, the conductive heat flux entering the wall can be directly computed without coupling with a solid conduction solver. Moreover, under this approximation, the pyrolysis gas mass flow rate is a known fraction of the char mass flow rate. Simulations of carbon-phenolic solid rocket motor nozzle have been performed to validate the model and to investigate the most uncertain parameters. Results show the influence of pyrolysis gas composition and ratio between mass fluxes of pyrolysis gas and of gaseous carbon, over the final erosion.