Navier-stokes simulation of graphite nozzle erosion under a wide range of pressure conditions

Ablative materials are commonly used to protect the nozzle housing and to provide the internal contour to expand the exhaust gases in solid rocket motors (SRM). Due to 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 erosion rate of graphite SRM nozzles under a wide range of pressure conditions for both metallized and non-metallized propellants. Recently, Evans et al. have performed extensive nozzle erosion rate measurements for G-90 graphite using an instrumented sub-scale solid rocket motor (ISPM) capable of performing tests at elevated pressure levels. Numerical simulations have been performed to reproduce some of the 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 which 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.