Acoustic modes of self-excited cavitating waterjets on rock erosion

This study experimentally investigates the impact of passive acoustic excitation modes from self-excited cavitating waterjet clouds on erosive patterns using high-speed imaging, scanning electron microscopy, and macroscopic three-dimensional scanning. Basalt, granite, and sandstone were used to study erosion and breaking mechanisms under various excitation modes, including sub-harmonic, fundamental, double-harmonic, and a case without feedback based on the primary cavitation cloud shedding frequency. Proper orthogonal decomposition of high-speed snapshots revealed that the cavitation cloud shed primary and secondary modes with passive acoustic excitation. The fundamental excitation mode promoted the primary cavitation cloud's volume and development, and energy transfers from secondary to primary modes resulted in the maximum cavitation cloud volume inducing the best rock-breaking ability. Macroscopic and microscopic inspection of the rock coupons' topographies revealed that the breaking mechanism involves a continuous peeling off of mineral grains under the cavitation cloud's impact.