[Seminar] Bubble clustering and the related phenomena by Prof. Shu Takagi

Speaker

Prof. Shu TAKAGI
The University of Tokyo

Shu Takagi is a Professor at Department of Mechanical Engineering and Department of Bioengineering, The University of Tokyo, since 2010. His areas of expertise include numerical simulations and experimental investigations on dispersed multiphase flows, especially bubbly flows and blood cell flows, medical ultrasound, micro-scale heat transfer, molecular thermo-fluid mechanics and multiscale analysis of thermo-fluid phenomena. He received his Ph.D. (1995) in Mechanical Engineering from the University of Tokyo. He became an Assistant Professor in 1998 and Associate Professor in 2002 at Department of Mech. Eng. the Univ. Tokyo. He was a Visiting Researcher at The Johns Hopkins University 1992-1993 and 2000-2001. He also worked as a Team Leader at RPCS, Organ and Body Scale Team, RIKEN (2007-2012). He is currently contributing as presidents of Japan Society of Fluid Mechanics and Japan Society of Multiphase Flows.

Title

Bubble clustering and the related phenomena

Abstract

Two Topics related to bubble clustering phenomena in liquid are presented. One is bubble clustering in upward bubbly flow. By controlling the small amount of surfactant, bubble clustering phenomenon can be observed in upward bubbly flow. This bubble cluster gives drastic change to bubbly turbulence and extinguishes large scale vortical structures in a turbulent boundary layer. In this talk, we discuss how the bubble cluster can change the large scale structures in turbulence. The other topic is a bubble cluster in focused ultrasound. Microbubbles are clinically used as a contrast agent for ultrasound diagnosis. These microbubbles have a potential to be used for drug delivery systems. Here, interesting microbubble clustering phenomena captured in the focal region of ultrasound are discussed. Since the focal region is stable for each microbubble, microbubbles start accumulating in the focal region and form a bubble cluster. This bubble cluster grows by attracting more bubbles in the cluster. However, this cluster disappears beyond a certain critical size of the bubble cluster. This phenomenon is discussed in more detail.