Cavitation microstreaming induced by sessile and pendent bubbles under confinement

Cavitation microstreaming is the steady, non-oscillatory flow induced by a bubble oscillating in an acoustic field. The present study investigates the underlying cause of streaming patterns generated in cavitation microstreaming. This work focuses on two configurations of the bubble: sessile and pendent. Bubbles of constant volume were placed in the cuboidal chamber, and the effect of the height of the chamber and the frequency of excitation was studied. The Energy Minimization Method was used to verify the shape of the stationary bubble. PIVlab in MATLAB was used to determine the velocity field obtained from Micro-Particle Image Velocimetry. We investigate the effect of confinement with rigid boundaries on flow fields seen in cavitation microstreaming. A flow regime map in the parameter space of chamber height and driving frequency for both sessile and pendent-type bubbles is presented. These maps would help experimentalists design and operate lab-on-chip devices for various applications, such as sonoporation, cell lysis, and micro-mixing. A key finding of this study is that there are two different physics that govern the flow field depending on the frequency of the acoustic excitation. Specifically, the streaming patterns are dominated by vibration-induced flow at low frequencies. On the other hand, acoustic pressure-induced interface deformation is dominant when the resonant frequency of the transducer coincides with that of the bubble.