Surface Instabilities and Nonspherical Oscillations of Bubbles in Ultrasonic Fields

Orateur : Matthieu GUÉDRA (LabTAU, INSERM Lyon, France)

Nonspherical bubble oscillations classically arise from the surface instability of an acoustically-driven bubble, through a mechanism similar to the hydrodynamic Faraday waves observed on a vertically-oscillating liquid layer. Although largely observed and reported for many years, the role played by these oscillations in various cavitation phenomena is not yet completely elucidated. To get a deeper insight into these nonspherical oscillations, we developed an experimental setup based on acoustic levitation and high-speed optical recordings of the bubble dynamics. First, I will present a set of experiments conducted using two synchronous high-speed cameras and discuss the axisymmetry properties of the surface modes. Then I will present two methods allowing to induce and control the nonspherical oscillations : (1) amplitude modulation of the ultrasonic field and (2) bubble coalescence. In both cases, the recorded temporal dynamics show evidence of nonlinear nonspherical oscillations which are supported by theoretical results obtained from recent models.

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