Numerical Simulation of a Near-Wall Bubble Collapse in an Ultrasonic Field

Abstract

Ultrasonic cleaning device was modeled and the collapse of a single bubble in an ultrasonic pressure field was studied using a finite-volume 2D axisymmetrical model. The pressure field was generated with the bottom of a container oscillating at 33 kHz. Spherical air bubble of resonance size was induced into water near the bottom where it violently collapsed. Compressibility of both phases was taken into account and the interface between air and water was captured using Volume-Of-Fluid approach. Maximal pressures, temperatures and velocities, generated during the collapse, were studied with regard to the initial bubble distance from the bottom. The results were compared for different time step sizes and grid densities where some great differences were found. For validation of the model a separate numerical simulation was run for a bubble collapsing near a rigid wall in a uniform pressure field. The computed bubble shapes were compared to the experimentally observed bubble shapes of Philipp and Lauterborn (1998) and a very good agreement was found. Although the collapse of just one bubble was studied, the results obtained gave good insight into conditions that happen due to cavitation in a near-wall region of ultrasonic cleaning devices.