To accurately assess the ablation behavior of solid rocket motor (SRM) nozzles under long-duration operating conditions and to reliably predict the wall ablation rate, a composite-structured nozzle was designed using carbon/carbon (C/C) and high-silica/phenolic composites, followed by a 76 s thermal-ablation firing test. In parallel, a dynamically coupled model accounting for both ablation and wall recession was developed based on FLUENT, incorporating a secondary development framework using user-defined functions (UDFs). Numerical simulations were conducted to investigate the heat transfer and ablation characteristics of the nozzle, with particular focus on wall ablation behavior. The results revealed pronounced ablation steps at the material interfaces in the convergent section. The measured average ablation rate in the throat straight segment was 0.00639  mm·s^-1, while the simulated rate was 0.00686  mm·s^-1, resulting in a deviation of 7.36%. The simulated wall temperature at the throat measurement point deviated by less than 15% throughout the test duration, thereby demonstrating the accuracy of the proposed numerical model. Ablation in the convergent section was primarily governed by the diffusion rate of reactive species, while in the throat and divergent sections, it was dominated by the thermochemical reactions rate. Among the oxidizing species, H₂O was identified as the principal contributor to material ablation.

Solid Rocket Motor,Multiple interface Nozzle,Ablation,Wall recession,Experimental research