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Synthetic jet generation by high-frequency cavitation
Published online by Cambridge University Press: 21 June 2017
Abstract
Cavitation bubbles are nucleated at a high repetition rate in water by delivering a pulsed laser through a fibre optic. Continuous high-frequency cavitation drives a stream away from the fibre tip. Using high-speed photography and particle image velocimetry, the stream is characterised as a synthetic jet, generated by trains of vortices induced by non-spherical bubble collapse. At low laser power, the bubbles collapse before the arrival of a subsequent laser pulse. Yet, by increasing the laser power, a system of bubbles is formed which leads to complex bubble–bubble interactions. The synthetic jet is observed regardless of the bubble formation regime, demonstrating the stability of the phenomenon. Synthetic jet generation by repetitive bubble collapse extends the well-studied acoustic streaming from small-amplitude bubble oscillations.
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- © 2017 Cambridge University Press
References
Mohammadzadeh et al. supplementary movie
Motion of fluorescent microparticles due to high-frequency cavitation on a fibre optic tip. A complex flow field is observed near the tip, with particles going back and forth as bubbles form and collapse. The particles are radially attracted toward the fibre axis, driving a jet that is directed away from the cavitation site. The laser is running at 40 kHz and 20 W.
Mohammadzadeh et al. supplementary movie
Bubble formation at the tip of a fibre optic that delivers a pulsed laser at a repetition rate of f=40kHz into water. From top to bottom, the average laser power P=2.5, 5, 10, and 15W. At low laser power, the bubble collapses before the next laser pulse. However, by increasing the laser power, the bubble grows large enough such that it has not collapsed when the next laser pulse arrives. This leads to formation of a secondary bubble at the tip of the initial bubble, which moves away from the fibre tip as it collapses.
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