High-speed imaging of an ultrasound-driven bubble in contact with a wall: “Narcissus” effect and resolved acoustic streaming |
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Authors: | Philippe Marmottant Michel Versluis Nico de Jong Sascha Hilgenfeldt Detlef Lohse |
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Affiliation: | (1) Department of Science and Technology, University of Twente, P.O. Box 217, 7500 Enschede, The Netherlands;(2) Department of Experimental Echocardiography, Thoraxcentre, Erasmus MC, Rotterdam, The Netherlands;(3) Present address: Laboratoire de Spectrométrie Physique, CNRS-Université Joseph Fourier, BP 87, 38402 Saint Martin d’Hères, France;(4) Present address: Engineering Sciences & Applied Mathematics and Department of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA |
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Abstract: | We report microscopic observations of the primary flow oscillation of an acoustically driven bubble in contact with a wall, captured with the ultra high-speed camera Brandaris 128 (Chin et al. 2003). The driving frequency is up to 200 kHz, and the imaging frequency is up to 25 MHz. The details of the bubble motion during an ultrasound cycle are thus resolved, showing a combination of two modes of oscillations: a radius oscillation and a translation oscillation, perpendicular to the wall. This motion is interpreted using the theory of acoustic images to account for the presence of the wall. We conclude that the bubble is subjected to a periodic succession of attractive and repulsive forces, exerted by its own image. Fast-framing recordings of a tracer particle embedded in the liquid around the particle are performed. They fully resolve the acoustic streaming flow induced by the bubble oscillations. This non-linear secondary flow appears as a tiny drift of the particle position cycle after cycle, on top of the primary back and forth oscillation. The high oscillation frequency accounts for a fast average particle velocity, with characteristic timescales in the millisecond range at the lengthscale of the bubble. The features of the bubble motion being resolved, we can apply the acoustic streaming theory near a wall, which provides predictions in agreement with the observed streaming velocity. |
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