Investigating the mechanical erosion of the solid rocket motor convergent-divergent (C-D) nozzle is essential to overcome its development barriers. Consequently, the break-up mechanism of the aluminum oxide agglomerates was studied to determine the influence of the exhaust gas flow acceleration during the flight. Water and air flows were used as a substitute for aluminum oxide and exhaust gases. Experiments were conducted at different water flowrates and constant air velocity, where the results were used to validate a numerical model. The results revealed an excellent acceptance between the numerical, the experimental data (6–19%), and the effect of increasing the water flowrate on the break-up mechanism. The validated numerical model was further used to study the airflow acceleration impact on the break-up process. It was found that applying acceleration to the airflow subjects the water surface to rapid and sudden changes in the relative velocity between the gas and liquid, thus separating more water fragments from the primary liquid. In other words, it enhances the break-up process by reducing the average diameter with a range from 6.5% to 9% compared to the no-acceleration case and increasing the average droplets’ number (8.5–17%).