Radiation and Roughness Effects on Nozzle Thermochemical Erosion in Solid Rocket Motors

Surface roughness and radiation effects on the erosion behavior of a graphite nozzle are studied for both metallized and non-metallized propellants. A validated numerical approach that relies on a full Navier-Stokes flow solver coupled with a thermochemical ablation model is used for the analysis. A modification of the Spalart-Allmaras turbulence model is implemented to account for surface roughness. Net radiative heat flux is considered in the surface energy balance at the nozzle interface. Two different simplified models are used to evaluate the integral emissivity of dispersed alumina particles. Individual and combined effects of roughness and radiation are analyzed. Surface roughness enhances the erosion rate for both metallized and non-metallized propellants noticeably. The radiation influences the erosion rate of non-metallized propellant more than the metallized one, mainly due to the different erosion regimes, kinetically-controlled for the former and diffusion-controlled for the latter.