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Coherent structures in uniformly sheared turbulent flow

Published online by Cambridge University Press:  16 November 2011

Christina Vanderwel
Affiliation:
Department of Mechanical Engineering, University of Ottawa, Ottawa, Ontario, Canada, K1N 6N5
Stavros Tavoularis*
Affiliation:
Department of Mechanical Engineering, University of Ottawa, Ottawa, Ontario, Canada, K1N 6N5
*
Email address for correspondence: stavros.tavoularis@uottawa.ca

Abstract

Uniformly sheared turbulent flow has been generated in a water tunnel and its instantaneous structure has been examined using flow visualization and particle image velocimetry. The shear-rate parameter was approximately equal to 13 and the streamwise turbulence Reynolds number was approximately 150. The flow was found to consist of regions with nearly uniform velocity, which were separated by regions of high shear containing large vortices. The concentration of vortices and the distributions of their directions of rotation, strengths, sizes and shapes have been determined. These results demonstrate that horseshoe/hairpin-shaped vortices were prevalent, even though wall effects were negligible in this flow. Both ‘upright’ and ‘inverted’ vortices have been observed, in contrast to turbulent boundary layers, in which only ‘upright’ vortices can be found, suggesting that the presence of the wall may suppress the development of ‘inverted’ structures. Our observations demonstrate that the dominant coherent structures of fully developed uniformly sheared flow are very different from the structures observed in the flow exiting the shear-generating apparatus, which points to an insensitivity of the former to initial effects.

Type
Papers
Copyright
Copyright © Cambridge University Press 2011

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