Carbon-Carbon Nozzle Erosion and Shape Change in Full-Scale Solid-Rocket Motors

The erosion of nozzle protection materials during solid-rocket-motor burning needs to be accounted for to get reliable performance predictions, especially for long-duration firings. A study is conducted to predict carbon-carbon nozzle erosion behavior in full-scale solid-rocket motors for wide variations of motor operating conditions. The numerical model considers the solution of Reynolds-averaged Navier-Stokes equations in the nozzle, heterogeneous chemical reactions at the nozzle surface, ablation species injection in the boundary layer, variable multicomponent transport and thermodynamic properties, and heat conduction in the nozzle material. Two different ablation models are considered: a diffusion-limited approach and a finite-rate approach. The numerical model is used to study the erosion of carbon-carbon nozzle inserts for the second- and third-stage solid-rocket motors of the European Vega launcher. The effect of variable chamber pressure over the burning time and the effect of nozzle shape change on the erosion rate are taken into account in the numerical analysis. The obtained results show a very good agreement with the measured final eroded profile along the entire carbon-carbon nozzle throat insert for both motors. The shape-change effect is shown to be an important factor that has to be taken into account to get a good prediction of the throat erosion for long-duration firings.