Research on the mechanism and morphology of coal damage by water jet deflection angle

This study investigates coal damage mechanisms under water jet deflection angles of 0°, 30°, 45°, and 60° through theoretical analysis, numerical simulation, laboratory experiments, and field validation. Theoretical analysis revealed that jet angle significantly affects velocity decomposition and water accumulation, influencing damage characteristics. Numerical simulations using LS-DYNA demonstrated that damage depth decreases while damage width increases with increasing jet angle. Coal damage volume peaked at 45°, being 127% greater than vertical jetting. Laboratory experiments confirmed these patterns, with coal output following the trend: 45° (225 g) > 30° (206 g) > 60° (182 g) > 0° (99 g). Field tests at Zhaojiazhai Mine validated that 45° jetting achieved optimal coal removal (3.25t average), 141% higher than vertical jetting (1.35t). These findings provide quantitative guidance for optimizing hydraulic slotting operations, with 45° identified as the optimal angle for maximizing coal damage volume while balancing depth and width considerations.