Curtiss, Geoffrey Aylwyn (2009)
Ph.D. thesis, University of Birmingham.
The interactions of bubbles with rigid and free boundaries have been well documented. Toroidal bubble formation has been observed, with jetting directed toward and away from the two types of interface respectively. This work generalises these interactions by studying the effect of a two fluid interface supporting a density discontinuity. Such interactions may provide significant new insight into the mechanisms present in bubble assisted mixing processes, and in biomedical procedures including laser ablation and sonoporation. A numerical investigation has been conducted to examine the essentially incompressible fluid dynamics of the exterior liquid layers, based on a boundary integral implementation coupled with the vortex ring toroidal bubble model . The transition through the null impulse state has been investigated, demonstrating excellent agreement with the water/white spirit experiments of Chahine and Bovis . Close standoff distance simulations have illustrated the retardation of surface spiking with increasing density ratios, and have shown how the toroidal phase can be beneficial to mixing processes. Multi-bubble simulations have demonstrated that the deformation to the interface is greatly affected by the configuration of the bubble column. The acoustic driving of ultrasound contrast agents near tissue layers has also been investigated, demonstrating a new mechanism for tissue damage due to the toroidal re-expansion, the membrane peeling phenomenon.
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