Jet reversal and bubble dynamics near gas-entrapped surfaces

We studied the bubble and resulting jet dynamics near gas-entrapped surfaces experimentally using spark-induced bubbles with a radius of a centimeter and high-speed photography. We found three distinct jetting behaviors, namely direct toward the boundary, direct backward the boundary, and split both toward and backward, which is determined by three dimensionless parameters, i.e., depth (H̃) and cross section area (Ã) of the gas cylinder and the standoff distance (γ) of the bubble. Bubble lifetime, maximum radius, and impact velocity of the penetrated jet on the bubble are also investigated. Furthermore, the non-dimensional volume (α) of gas entrapped on the rigid boundary is the dominant parameter in the jet reversal, larger α leads to a stronger reverse. The results and conclusions in this study are useful for resisting cavitation erosion.