Bubble size measurements in different acoustic cavitation structures: Filaments, clusters, and the acoustically cavitated jet

•New method to measure bubble equilibrium sizes in acoustic cavitation structures using high-speed Imaging.•For several experimentally realized bubble structures, the distributions of bubble equilibrium radii are presented.•Abundant cavitation is experimentally produced by sonication of a slow submerged jet; the processes are numerically explored. Acoustic cavitation typically forms a variety of bubble structures of generally unknown and broad size distributions. As the bubbles strongly oscillate, their (equilibrium) sizes are not directly observable. Here, a method is presented to experimentally determine the size distribution in bubble populations from high-speed imaging of the bubbles in oscillation. To this end, a spherical bubble model is applied in statistical fashion. This technique is applied to several experimentally realized bubble structures: streamer filaments, clusters, and a peculiar structure we report here on, the acoustically cavitated jet. It is generated by the sonication of a submerged jet to produce abundant cavitation at low flow velocities. Our analysis is complemented by numerical exploration of the hydrodynamic and acoustic properties of the experimental configuration in which the observed bubble structures are formed.