Numerical analysis of nozzle flows with finite-rate surface ablation and pyrolysis-gas injection

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 (SRM). Due to the extremely harsh environment in which these materials operate, they are chemically eroded during motor firing with a resulting nominal performance reduction. The objective of the present work is to study the erosion behavior of carbon-phenolic solid rocket 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 ablation species injection in the boundary layer, heat conduction inside the nozzle material, and variable multispecies thermophysical properties. The proposed approach is validated against two sets of experimental data: sub-scale 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 carbon-phenolic for the region downstream of the throat. © 2011 by D. Bianchi, A. Turchi and F. Nasuti.