Numerical Simulation of Carbon-Carbon Erosion in SRM Nozzles

The erosion of rocket-nozzle materials during motor firing is one of the major hindrances in the advancement of solid-rocket propulsion. A study is conducted to predict Carbon-Carbon nozzle erosion behavior in solid rocket motors for wide variations of propellant formulations. The numerical model considers the solution of Reynolds averaged Navier-Stokes equations in the nozzle, heterogeneous chemical reactions at the nozzle surface, variable transport and thermodynamic properties, and heat conduction in the nozzle material. Two different ablation models are considered: a surface equilibrium approach and a finite-rate model. Results show that the erosion rate is diffusion-limited for metallized propellants ensuring sufficiently high wall temperatures and is kinetic-limited when wall temperature drops below a limiting value. For high surface temperatures the two models are consistent with each other and predict the same erosion rate, while the surface equilibrium model over predicts the recession at low surface temperatures. The calculated results show an excellent agreement with the experimental data from the BATES motor firings and the finite-rate model actually improves the predictions when the kinetic-limited regime is approached. The model is used to study the nozzle erosion of the VEGA launcher third stage motor, Zefiro 9, showing a very good agreement with the receded profile along the entire carbon-carbon nozzle throat insert.