 ?Multi-bubble clusters in sonoluminescence for a cylindrical resonator and bi-harmonic driving?

JUAN MANUEL ROSSELLO,; DAMIAN DELLAVALE; BONETTO, FABIAN

Workshop; XIII Latin American Workshop on Nonlinear Phenomena (LAWNP); 2013

In the present work, bubble clusters formed of multiple sonoluminescent bubbles were experimentallyand theoretically studied. Argon bubbles were acoustically generated and trapped using a bi-harmonic pressurefield within a cylindrical acoustic chamber filled with sulphuric acid (SA85w/w). This acoustic pressure fieldwas strong enough to sustain, for long periods of time, an ellipsoid shaped tridimensional cluster formed by alarge number of spatially fixed SL bubbles. In order to explain the size and shape of the bubble clusters, weperformed a series of numerical simulations of the hydrodynamic forces acting over the individual bubbles,where bubble-bubble interaction has been neglected. The results revealed that the positional stable region isdefined as an axisymmetric ellipsoidal surface centered in the acoustic field antinode, and is mainly determinedby the null Bjerknes force (FBj=0). The dimensions of the ellipsoids were studied as a function of the appliedlow frequency acoustic pressure amplitude (PAcLF) and the static pressure of the fluid (P0). In both cases theobserved experimental behavior was in agreement with the simulation results. As PAcLF is increased the surfaceexpands in order to preserve the conditions were the net force acting on the bubble is zero. We also found asignificant reduction of the cluster dimensions as P0 was augmented. The later is a direct consequence of theshift occurring in the positional stability frontier to regions with high PAcLF as P0 is increased.