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The release of air bubbles from an underwater nozzle

Published online by Cambridge University Press:  26 April 2006

Michael S. Longuet-Higgins
Affiliation:
Institute for Nonlinear Science, University of California, San Diego, La Jolla. CA 92093, USA
Bryan R. Kerman
Affiliation:
Canada Centre for Inland Waters, Burlington, Ontario L7R 4AL, Canada
Knud Lunde
Affiliation:
Department of Applied Mathematics and Theoretical Physics. Silver Street, Cambridge CBS 9EW, UK

Abstract

Air bubbles released from an underwater nozzle emit an acoustical pulse which is of interest both for the study of bubble detachment and for elucidating the mechanism of sound generation by a newly formed bubble. In this paper we calculate theoretically the sequence of bubble shapes from a given nozzle and show that there is for each nozzle a bubble of maximum volume vmax Assuming that the bubble becomes detached at its ‘neck’, and that the volume of the detached bubble equals the volume V* of the undetached bubble above its ’neck’, we determine for each nozzle diameter D an acoustic frequency f* corresponding to 'slow’ bubble release.

Experiments show that the acoustic frequency, hence the bubble size, depends on the rate of air.flow to the bubble, but for slow rates of flow the frequency f is very close to the theoretical frequency f*.

High-speed photographs suggest that when the bubble pinches off. the limiting form of the surface is almost a cone. This is accounted for by assuming a line sink along the axis of symmetry. Immediately following pinch-off there is evidence of the formation of an axial jet going upwards into the bubble. This may play a part in stimulating the emission of sound.

Type
Research Article
Copyright
© 1991 Cambridge University Press

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