Effect of axial ullage distribution of modular charges on the dynamic behavior of cylindrical particles in the combustion chamber

The modular charge is a novel charge system designed to cooperate with the automation of large-caliber guns. Using Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM), the motion and distribution of cylindrical particles driven by high-temperature, high-pressure gas during ignition and flame spreading were simulated in a two-module charge. Model validation was achieved through comparison with experimental data from simulated ignition experiments. Different ullage distributions were achieved by varying the axial distance between the primer and the first module. The results indicate that while maintaining a constant axial ullage between Module 1 and Module 2 (D₂), increasing the axial distance between Module 1 and the primer (D₁) leads to distinct changes in the particle packing structure. Particles stabilize in horizontal and steep slope accumulations from the breech to the front end of the combustion chamber in a stable state. However, the axil length of horizontal accumulation decreases linearly with increasing D₁, and the axil length of steep slope accumulation shows a second-order polynomial relationship with D₁. The inclination angle of the steep slope initially decreased and then increased. Axial ullage distribution affects the forces on the particles, velocities, and trajectories, resulting in uneven distribution within the combustion chamber.