Single cavitation bubble dynamics in a confined planar flow

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 ⋅ 1 0 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. • The flow alters the expansion and collapse of laser-induced bubbles near boundaries. • The flow breaks axi-symmetry and the bubble sites deform differently. • Near the boundary, the bubble forms a jet that is angled relative to the flow. • At higher flows, the bubble lifts off partly and collapses away from the boundary.