Water Hammer Characteristics of Self-Rotating Cascade Jets Impacting on Rock

Water jets impacting the rock cause water hammer effects, resulting in significant damage to the rock. The self-rotating cascade jet breaks rocks through rotational impact, but its water hammer characteristics are still uncertain. The models for water hammer pressure and its duration and dimensionless action length of a cascade jet were constructed using dynamic elasticity and analytic geometry. Moreover, rock-breaking experiments were conducted using a developed cascade nozzle bit to validate the models. The results show that the impact of self-rotating cascade jets on the rock does not generate continuous water hammer pressure. The water hammer characteristics and rock-breaking capacity of the designed jets are ranked as follows: the central jet is the strongest, the first cascade jet is the second strongest, and the second cascade jet is the weakest. The characteristics of the water hammer and rock-breaking capacity for the self-rotating cascade jet increase as the rotational speed and the eccentric distance decrease, the pressure, the impact angle, and the radius increase. The results can lay a theoretical foundation for understanding the rock-breaking mechanism of the self-rotating cascade jet and developing new types of pulsed jets.