Coupled Analysis of Flow and Surface Ablation in Carbon-Carbon Rocket Nozzles

A study is conducted to predict carbon–carbon nozzle recession behavior in solid rocket motors for wide variations of propellant formulations and 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, variable transport and thermodynamic properties, and heat conduction in the nozzle material. Results show that the ablation rate is largely determined by the diffusion of the major oxidizing species (H2 O, CO2 , OH) to the nozzle surface. Both the concentration of the major oxidizing species (affected by the aluminum content of the propellant) and the chamber pressure exert a strong influence on the ablation rate: it increases almost linearly with chamber pressure and it decreases with increasing aluminum content of propellants. The calculated results show an excellent agreement with the experimental data from the ballistic test and evaluation system motor firings.