In most practical applications, bubbles appear as clusters, filaments, and clouds rather than isolated bubbles. The cavitating flows and ultrasonic cleaning processes also produce numerous tiny bubbles. The dynamic behaviour of these bubbles in the cavitation cloud with mutual interactions is more complex than that of a single bubble.
This work attempts to understand the complicated dynamics of interacting cavitation bubbles and resulting liquid microjets. Additionally, we have unravelled the mechanism of high-speed microjets. It suggests that the rebounding top bubble after its collapse imparts momentum by transmitting the pressure energy to the confined liquid (primary motion) that lead to the onset of the jet motion in the bottom bubble. The inertial focusing of flow (secondary motion) on the bottom bubble accelerates the micro-jet even further, culminating in a strong jet.
As observed in this work, the directional microjets can generate strong mechanical shearing and are suitable for cell sonoporation, targeted drug delivery and can also erode certain plastics, polymers, and metals.
*Supported by the Computational Mechanics Group at Department of Mechanical engineering, IIT Kharagpur, India; Multiphase Fluid Dynamics laboratory at D-MAVT, ETH Zurich, Switzerland, and ETH4D Visiting Student Grant, ETH for Development, Zurich.