Single cavitation bubble dynamics in a confined planar flow

Abstract

Single cavitation bubbles are nucleated in a planar flow within a narrow liquid filled gap to understand the effect of velocity gradients on the cavitation bubble collapse. The cavitation bubble is created close to one of the boundaries with a pulsed laser and near the center of the gap. Overall, the flow transports the center of mass of the bubble and induces a non-axisymmetric collapse that affects the direction and strength of the liquid jet. The water flow velocity is varied up to 18 m/s and resulting in shear rates of up to $4\cdot 10^5$1/s. Already at a moderate flow velocity of a few meter per seconds, the bubble looses its cylindrical symmetry when expanding and collapsing near the boundary. Additionally, the downstream region of the bubble lifts away from the boundaries, adding a thin layer of liquid between the jet and the wall. A bubble expanding in the center of the gap also looses its cylindrical symmetry that results in much weaker or no jets impacting on the boundaries. Overall, with increasing flow velocity the lifetime of the bubble is shortened, and its first collapse is occurring further away from the boundary.