Creation of a cluster of cavitation bubbles using diffusing droplets and its extension to sonoluminescence

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The purpose of the present research program is to investigate experimentally how a viscous droplet, injected into water, plays a role in creating many bubbles, which may eventually result in a single bubble. The process is complicated and difficult to manage, as noted by Naser Harba. More fundamental investigation has thus been carried out.1)Hydrodynamical behavior of a viscous diffusing droplet.First, with no ultrasound droplets of glycerol were let fall from a position 5 mm above the surface, but the droplets floated as long as its density was heavier than the solution by less than 0.02 g/cm^3. Diffusion may have helped to gain the buoyancy. Next, if ultrasound was applied, the droplets evaded the position where bubbles were otherwise trapped, suggesting that Naser Harba painstakingly observed those diffusing processes.2)Analysis of light-scattering data and related subjects.Mie-scattering data for multiple bubbles formed from an injected glycerol droplet were analyzed, with the assumption that bubbles obeyed the Rayleigh-Plesset equation. It turned out that the scattering data were affected by saturation due to light. Computer programs were developed for analysis of bubbles and drops and for jittering of pulses on the digital oscilloscope, which may mislead to false time-train signals.3)Sonoluminescence from concentrated sulfuric acid.Sulfuric acid is also viscous, and sonoluminescence from it was investigated at several frequencies.4)Numerical simulation of Moire patterns for diffusing dropletsMoire patterns were produced for a distribution of refractive index, which might mimic droplets isotropically diffusing within water.