Dynamics of wall attached bubbles excited by an acoustic field

We investigate oscillations of gas filled bubbles at a solid boundary. The bubbles are excited by an acoustic field with frequency 20 kHz and an amplitude of 0.9 bar. Bubble sizes range from 30 to 140 μm in initial radius. A finite volume method with a volume of fluid method is used to simulate the dynamics in an axially symmetric setting. We investigate the first two bubble oscillations. The computed bubble dynamics is rich. We observe the repeated formation of thin, fast jets after liquid self-impact at the axis during the collapse phases. Depending on the bubble size, smaller or larger bubbles are split off at liquid self impact. The bubble may lift off from the solid during the second collapse. Pairs of fast jets can be formed. Jets directed away from the solid are observed, in particular during the second rebound.