Fast jets from bubbles close to solid objects: examples from pillars in water to infinite planes in different liquids

Abstract

The dynamics of a single, laser-induced cavitation bubble on top of a solid cylinder and right at a plane solid boundary is studied both experimentally and numerically. The most intriguing phenomenon that occurs for a millimeter sized bubble right at a flat solid boundary in water is the formation of a fast jet that is directed towards the solid with a speed of the order of 1000 m/s. Paradoxically, in this setting, fast jet formation causally is related to the viscosity of the liquid.Thus, results from numerical simulations with varying liquid viscosity and bubble size are presented. Bubble dynamics and jet formation mechanisms are discussed. It is shown, that fast jet formation persists for a wide range of liquid viscosities, including e.g. 50 cSt silicone oil. For bubbles generated close to the flat top of a long, thin cylinder the parameter space of initial distance to the cylinder, bubble size and cylinder radius is scanned numerically and partly compared to experiments. When the maximum radius of the bubble exceeds the one of the cylinder the bubble collapses in the form of a mushroom or can resemble a trophy, depending on the values of the geometry parameters. Complex patterns of jet formation with jet speeds ranging from the order of a few hundred m/s to several thousand m/s are found.The results represent a contribution to understand the behavior of bubbles collapsing close to solid surfaces, in particular, how thin, fast jets are generated.