Abstract (Invited)

Micro Bubble and Bubble Cluster Dynamics in Ultrasound Field

Y.Matsumoto (Department of Mechanical Engineering, The University of Tokyo, Tokyo, Japan)

e-mail: ymats@mech.t.u-tokyo.ac.jp

The behavior of micro bubble cluster in an ultrasound field has non-linear futures and multiple scale structures in time and spatial. It is required to analyze the phenomena combining those scales reasonably. The bubble size is the micro-scale, the distance between bubbles is the mezzo-scale and the characteristic length in bubbly liquid, such as wave length, is the macro scale. The pressure wave phenomena in bubble cloud are simulated numerically taking micro and mezzo scale phenomena into account. The volumetric changes of bubbles are calculated in detail and found that they are significantly influenced by the internal phenomena, such as thermal diffusion, mass diffusion between vapor and non-condensable gas, heat and mass transfer through the bubble wall. The behavior of bubble clouds is analyzed in ultrasound fields. An inward propagating shock wave is formed during the collapse of bubble cloud, and the shock wave and its precursor are focused at the cloud center area. These phenomena associate high frequent pressure oscillation and violent bubble collapses. Those bubble collapses emit high pressure peaks, which are several hundreds times larger than that of a single bubble collapse.

Section : 4