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RESEARCH PAPERS

Concentration Profiles in Shallow Turbulent Wakes

[+] Author and Article Information
R. Balachandar

Department of Civil Engineering. University of Saskatchewan, Saskatoon, Canada, S7N 5A9

M. F. Tachie

Department of Mechanical Engineering. University of Saskatchewan, Saskatoon, Canada, S7N 5A9

V. H. Chu

Department of Civil Engineering, McGill University, Montreal, Canada, H3A 2K6

J. Fluids Eng 121(1), 34-43 (Mar 01, 1999) (10 pages) doi:10.1115/1.2822007 History: Received February 18, 1998; Revised October 15, 1998; Online December 04, 2007

Abstract

The present study deals with the noninvasive measurement of concentration in the intermediate shallow turbulent wake region using a video-imaging technique. The flow depths considered in the present study are small compared to the width of the channel and the generated wakes are categorized as shallow. On the basis of the observed behavior, the waves are classified as deep-shallow wakes and shallow-shallow wakes. The topology of the dye concentration distribution in the near and intermediate wake region indicates that the vortex structure tends to be preserved when the flow depth is relatively high and the dominant eddy structures are similar to that noticed in conventional two-dimensional wakes. In shallow-shallow wakes, the conventional Karman vortex street appears to be annihilated or intermittent. The lateral concentration distribution at several axial stations covering the first thirty body widths are considered for analysis. The instantaneous concentrations are observed to be several times higher than the corresponding mean values. Attempts are also made to determine the paths traversed by the vortex cores and the vortex core convection velocity. The axial variation of the wake half-width with depth of flow is also examined. A model is developed to predict the spread of the wake with downstream distance from the test body. A friction length scale is introduced in the model to account for the influence of depth and bed friction on the development of the wake.

Copyright © 1999 by The American Society of Mechanical Engineers
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