J. Fluid Mech. (2009), vol. 624, pp. 255–279. c  2009 Cambridge University Press doi:10.1017/S0022112008005430 Printed in the United Kingdom 255 Growth, oscillation and collapse of vortex cavitation bubbles JAEHYUG CHOI 1 †, CHAO-TSUNG HSIAO 2 , GEORGES CHAHINE 2 AND STEVEN CECCIO 1 1 Department of Mechanical Engineering The University of Michigan, Ann Arbor, MI 48109-2121 USA 2 DYNAFLOW Inc., Jessup, MD 20794 USA (Received 11 August 2007 and in revised form 30 November 2008) The growth, oscillation and collapse of vortex cavitation bubbles are examined using both two- and three-dimensional numerical models. As the bubble changes volume within the core of the vortex, the vorticity distribution of the surrounding flow is modified, which then changes the pressures at the bubble interface. This interaction can be complex. In the case of cylindrical cavitation bubbles, the bubble radius will oscillate as the bubble grows or collapses. The period of this oscillation is of the order of the vortex time scale, τ V =2πr c /u θ,max , where r c is the vortex core radius and u θ,max is its maximum tangential velocity. However, the period, oscillation amplitude and final bubble radius are sensitive to variations in the vortex properties and the rate and magnitude of the pressure reduction or increase. The growth and collapse of three-dimensional bubbles are reminiscent of the two-dimensional bubble dynamics. But, the axial and radial growth of the vortex bubbles are often strongly coupled, especially near the axial extents of the bubble. As an initially spherical nucleus grows into an elongated bubble, it may take on complex shapes and have volume oscillations that also scale with τ V . Axial flow produced at the ends of the bubble can produce local pinching and fission of the elongated bubble. Again, small changes in flow parameters can result in substantial changes to the detailed volume history of the bubbles. 1. Introduction The static pressure in the core of a linear vortex is depressed when compared with the pressure far from the vortex axis. In some cases, when the vortex circulation is large enough, the pressure in the vortex core can fall below the liquid vapour pressure, and it is possible for negative pressures, or tensions, to exist in the core. Vortex cavitation occurs when a small bubble or nucleus explosively grows when exposed to these liquid tensions in the vortex core. Sometimes vortex cavitation bubbles remain small compared with the vortex core radius, with nearly spherical rapidly growing and collapsing bubbles entirely within the confines of the vortex core. However, if the bubble is exposed to a prolonged or severe application of tension, the initially near-spherical bubble can expand and elongate to fill the core of the vortex and continue to grow along the vortex axis, becoming highly elongated. The growth, splitting and collapse of vortex cavitation bubbles can produce easily detectable sound pulses (Choi & Chahine 2004, 2007; Hsiao & Chahine 2005; Choi & Ceccio 2007). † Email address for correspondence: choijh@umich.edu