A Dual-scale Model for Estimating the Ablation Rate of C/C Composite Nozzle

Based on the inherent ablation issues under the hostile thermochemical environment in solid rocket motors (SRM), a dual-scale ablation model of C/C composite nozzle is established. It investigates the ablation rate from both macroscopic and microscopic perspectives. The mechanical erosion of particles and the chemical reaction of gas are comprehensively considered. At macroscale, the turbulence model is proposed to obtain the temperature distribution and the flow field of the nozzle; the particle tracking model is applied to analyze the degree of mechanical erosion and it demonstrates 0.94% ~ 1.88% of the particles will eventually be deposited on the wall. At microscale, the regression and morphology of the surface of C/C composites are simulated by level set method, and the thermochemical ablation law of fibers and matrix is revealed. In addition, the influence of changes in microscopic morphology on surface reaction is input to the macroscale model, and a more convincing chemical ablation rate is evaluated. In the typical ablation conditions, the chemical ablation rate and mechanical erosion rate of the nozzle are respectively estimated as 0.03 mm/s and 0.0063 mm/s, which accords well with the reported data. Thus, our model identifies two extreme situations, i.e., when there are lots of Al₂O₃ particles, nozzle erosion is dominated by mechanical erosion, but when Al₂O₃ particles are very few, chemical ablation plays a major role. The limit ratio of mechanical erosion and chemical ablation are calculated. The results of the present study provide a deeper understanding of the ablation mechanism of C/C composite nozzle, which is useful for the thermal performance research and design of C/C nozzle.