Particle Approach to Structure Formation in Acoustic Cavitation

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Many gas bubbles emerge when a liquid is strongly sonicated [1]. At least some of them represent the active sites in sonochemistry and multibubble sonoluminescence. Each bubble shows an individual fast dynamics by volume and shape oscillations that are responsible for the specific chemical or luminescent process. However, a bubble field shows a collective dynamics on a slower time scale as well: nucleation, drift, diffusion, coalescence and destruction picture a bubble’s life, and many of such histories determine the bubble distribution in space and time. Experiments reveal that this distribution in typical applications is far from homogeneous. On the contrary, the bubbles tend to organize themselves in filaments (“streamers”) that can form complex tree-like structures (in analogy to electrical discharge patterns we call them “Acoustic Lichtenberg Figures” or ALFs; see Fig. 1). The inhomogeneous bubble population in strong sound fields is a major complication for the investigation, modeling and enhancement of sonochemical processes, and more insight in the underlying mechanisms are of high demand. Here we report a first step towards a simulation of bubble structure formation by a many particle approach. The basis are recent calculations of Bjerknes forces in strong acoustic fields that govern the bubble motion [2,3].