Cavitation in water jet under high ambient pressure conditions

Abstract

Cavitating jet has been widely used in underground drilling to enhance the rock erosion efficiency. In this circumstance, the high ambient pressure directly influences the bubble traveling process and cavitation impact pressure. To quantitatively assess the erosion intensity of the cavitating jet under the high ambient pressure conditions, a combined numerical and experimental investigation was conducted. A convergent-divergent nozzle was chosen to generate the cavitating jet in a closed test cell. A bubble transportation model was used to simulate the bubble traveling in the water jet through the nozzle and investigate the effects of ambient pressure and flow rate on the transportation efficiency. Pitting analysis with specimen 7075 aluminum alloy was performed to measure the magnitude and distribution of the cavitation impact pressure at different standoff distances. The results reveal the dynamic bubble traveling process and shed light on the cavitation impact field. The bubble transportation capability of the cavitating jet depends on the jet velocity. Given certain ambient pressure and nozzle size, the flow rate must be larger than a certain threshold value for allowing the bubbles to be transported out before collapsing inside the nozzle. The magnitude of cavitation impact pressure is of the order of 1GPa and shows little dependence on standoff distance. However, the overall impact rate and the distribution pattern are significantly influenced by the standoff distance. It is concluded that the variation of the erosion intensity of cavitating jet correlates more closely with the change of the impact rate than with the absolute impact magnitude.