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Vortex pairing : the mechanism of turbulent mixing-layer growth at moderate Reynolds number

Published online by Cambridge University Press:  29 March 2006

C. D. Winant  and
F. K. Browand
C. D. Winant
Affiliation:
Division of Engineering and Applied Mechanics, University of Southern California, Los Angeles, California 90007 Present address: Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92037.
F. K. Browand
Affiliation:
Division of Engineering and Applied Mechanics, University of Southern California, Los Angeles, California 90007
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Abstract

A mixing layer is formed by bringing two streams of water, moving at different velocities, together in a lucite-walled channel. The Reynolds number, based on the velocity difference and the thickness of the shear layer, varies from about 45, where the shear layer originates, to about 850 at a distance of 50 cm. Dye is injected between the two streams just before they are brought together, marking the vorticity-carrying fluid. Unstable waves grow, and fluid is observed to roll up into discrete two-dimensional vortical structures. These turbulent vortices interact by rolling around each other, and a single vortical structure, with approximately twice the spacing of the former vortices, is formed. This pairing process is observed to occur repeatedly, controlling the growth of the mixing layer. A simple model of the mixing layer contains, as the important elements controlling growth, the degree of non-uniformity in the vortex train and the ‘lumpiness’ of the vorticity field.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 63 , Issue 2 , 3 April 1974 , pp. 237 - 255
Copyright
© 1974 Cambridge University Press

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