Cavitation erosion from single acoustically driven bubbles

Acoustic cavitation is achieved by exciting mechanical vibrations at ultrasonic frequencies, which in turn cause the formation of bubble clouds, followed by flows and emulsification. Typically, the effects of acoustic cavitation clouds on cleaning and erosion are difficult to predict or model due to the complex interactions among numerous bubbles. Systematic studies of acoustic cavitation bubbles are simplified by using single cavitation bubbles as a means of controlled cavitation, owing to their precisely defined timing and properties, which can be induced within an acoustic field by seeding a small laser-induced bubble within it. This work presents findings on the erosion of solid surfaces initiated by a single acoustic bubble. Optical seeding of a small cavitation bubble is combined with acoustic driving under a sonotrode tip to generate a single, controlled, and isolated acoustically driven bubble oscillating near a solid boundary. The phase delay and spatial coordinates of optical seeding within the acoustic field are explored to achieve repeatable acoustic bubble behavior with multiple expansion-collapse cycles as a single bubble before transitioning into a bubble cloud composed of multiple smaller bubbles. Using an ultra-high-speed camera and a hydrophone pressure sensor, bubble collapses are quantified in terms of shockwave energy and position. Finally, the resulting erosion patterns on the aluminum surface are measured using confocal laser surface scanning after multiple event repetitions. This technique enables the study of erosion patterns produced by temporally and spatially confined acoustically driven bubbles.