Chemical Erosion of Carbon-Phenolic Rocket Nozzles with Finite-Rate Surface Chemistry

Ablative materials are 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 eroded during motor firing with a resulting nominal performance reduction. The objective of the present work is to study the thermochemical erosion behavior of carbon-phenolic material in solid rocket motor nozzles. 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, pyrolysis gas and char-oxidation product species injection in the boundary layer, heat conduction inside the nozzle material, and variable multispecies thermophysical properties. The results obtained with the proposed approach are compared with two sets of experimental data: subscale motor tests carried out for the space shuttle reusable solid rocket motor and the static firing tests of the second and third stage solid rocket motors of the European Vega launcher, which use carbon-carbon for the throat insert and carbonphenolic for the region downstream of the throat.