Ablation performance of a 4D-braided C/C composite in a parameter-variable channel of a Laval nozzle in a solid rocket motor

Ablation of a 4D-braided C/C composite fabricated with axial rods in the parameter-variable channel of a Laval nozzle (or a convergent-divergent nozzle, a tube that is pinched in the middle) was performed in the experimental conditions of a solid rocket motor. Gas-solid flow and erosion were also simulated with the discrete phase model. The ablation of the composite was caused by thermochemical and mechanical erosion and was analyzed based on the morphology of different sections of the channel in the nozzle with different angles between the gas flow direction and the surface of the composite (ablation angle). Results showed that the ablation behavior was related to the velocity, concentration, collision angle to the surface and the wall shear force of particles in the ablation gas. The ablation gradually increased with the rate of gas flow and was a maximum at the maximum ablation angle of 45° in the compression section. In the expansion section, beyond the throat, ablation decreased significantly. The maximum linear and mass ablation rates were 0.056 mm/s and 0.157 kg/m2·s, respectively. The carbon fibers formed a tapered tip, whose sharpness depended on the ablation angle and the braiding direction.