Experimental study of the liquid flow near a single sonoluminescent bubble

Tracers (sulphur particles produced in situ by a bubble itself, fuchsin spots and dust) were used to probe the liquid flows in the neighborhood of single sonoluminescent bubbles maintained in levitation in a resonant acoustic setup. The flows caused by the bubble were distinguished clearly from the streamings (mean Lagrangian velocity: similar to 20 mu m/s) associated with resonant cells in the absence of a bubble. The liquid flow due to the presence of the bubble formed around it over a few mm. The radial component of the Lagrangian velocities (maximum value measured: similar to 260 mu m/s) of this flow evolved as r(-1), with r as the distance from the bubble, while the tangential component remained approximately constant (similar to 20 mu m/s). In the Appendix by M. S. Longuet-Higgins, a simplified model of microstreaming involving a spherical bubble in translational and radial oscillation gives a qualitative description of the experiments. A fairly good agreement was observed between the experiments and the modeling, which involved a dipole flow enclosed in a Stokeslet. (C) 2000 Acoustical Society of America. [S0001-4966(00)03207-0].