Navier–Stokes simulation of graphite nozzle erosion at different pressure conditions

Graphite is commonly used to protect the nozzle metallic housing and to provide the internal contour to expand the exhaust gases in solid rocket motors. Because of the extremely harsh environment in which these materials operate, they are chemically eroded during motor firing, with a resulting performance reduction. The objective of the present work is to study the thermochemical erosion of graphite nozzles under a wide range of pressure conditions for both metallized and nonmetallized propellants. Numerical simulations are performed to reproduce recent literature experimental tests for nominal chamber pressures up to 250 bar. The adopted approach relies on a validated full Navier–Stokes flow solver coupled with a thermochemical ablation model that takes into account finite-rate heterogeneous chemical reactions at the nozzle surface, rate of diffusion of the species through the boundary layer, ablation species injection in the boundary layer, heat conduction inside the nozzle material, and variable multispecies thermophysical properties. Results show that numerical simulations are able to correctly evaluate the erosion rate, provided that modeling aspects such as entrance length and combustion efficiency are suitably accounted for.