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Research Papers: Fundamental Issues and Canonical Flows

PIV-POD Investigation of the Wake of a Sharp-Edged Flat Bluff Body Immersed in a Shallow Channel Flow

[+] Author and Article Information
Arindam Singha

Department of Mechanical Engineering, University of Windsor, Windsor, N9B 3P4, Canadasingha2@uwindsor.ca

A.-M. Shinneeb

Department of Civil and Environmental Engineering, University of Windsor, Windsor, N9B 3P4, Canadashinneeb@uwindsor.ca

Ram Balachandar

Department of Civil and Environmental Engineering, University of Windsor, Windsor, N9B 3P4, Canadarambala@uwindsor.ca

J. Fluids Eng 131(2), 021202 (Jan 09, 2009) (12 pages) doi:10.1115/1.3054283 History: Received November 01, 2007; Revised June 22, 2008; Published January 09, 2009

This paper reports particle-image velocimetry measurements of instantaneous velocity fields in the wake of a sharp-edged bluff body immersed vertically in a shallow smooth open channel flow. The maximum flow velocity was 0.19 m/s and the Reynolds number based on the water depth was 18,270. The purpose of the present study is to show the vertical variation of the velocity field in the near region of a shallow wake. Measurements of the flow field in the vertical central plane and in the horizontal near-bed, mid-depth, and near-surface planes were taken. Then, the mean flow quantities such as the mean velocity, turbulence intensity, and Reynolds stress fields were investigated. In addition, the proper orthogonal decomposition technique was used to reconstruct the velocity fields to investigate the energetic vortical structures. The results showed that the largest recirculation zone in the mean velocity fields occurred in the mid-depth velocity field, while the smallest one occurred near the bed. Also, the fluid was entrained from the sides toward the wake central plane in the three horizontal velocity fields but with different rates. This behavior was attributed to the existence of quasi-streamwise vortices near the boundaries. In addition, patterns of ejection and sweep events near the free surface similar to the features commonly observed near the wall-bounded flows were observed.

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic showing (a) side view and (b) top view of the bluff body in the flume and the position of the four fields-of-view (not to scale)

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Figure 2

Mean streamwise velocity distribution of the smooth channel flow using inner and outer coordinates

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Figure 3

Streamline patterns of the mean velocity fields in the wake of the bluff body for three horizontal planes: (a) y/H=0.10, (b) y/H=0.51, and (c) y/H=0.76

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Figure 4

Development of the mean streamwise velocity U/Us in the streamwise direction x/D at different horizontal planes: (a) y/H=0.10, (b) y/H=0.51, and (c) y/H=0.76

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Figure 5

Development of the mean transverse velocity W/Us in the streamwise direction x/D at different horizontal planes: (a) y/H=0.10, (b) y/H=0.51, and (c) y/H=0.76

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Figure 6

A vector plot representing the mean flow field in the three horizontal planes (y/H=0.10, 0.51, and 0.76) superimposed by a gray contour of the normalized mean transverse velocity W/Us

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Figure 7

Variation of the normalized mean central velocity Uc/Us with downstream distance x/D

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Figure 8

Variation of the wake half-width z0.5/D with downstream distance x/D

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Figure 9

Development of the relative streamwise root-mean-square velocity Urms/Us in the normalized streamwise direction x/D for horizontal planes at (a) y/H=0.10, (b) y/H=0.51, and (c) y/H=0.76

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Figure 10

Development of root-mean-square transverse velocity Wrms/Us in the streamwise direction x/D for horizontal planes at (a) y/H=0.10, (b) y/H=0.51, and (c) y/H=0.76

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Figure 11

Development of turbulent kinetic energy K/Us2 in the streamwise direction x/D for horizontal planes at (a) y/H=0.10, (b) y/H=0.51, and (c) y/H=0.76

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Figure 12

Variation of Urms/Wrms in the streamwise direction x/D. The three curves were extracted from the three horizontal planes along the vertical central-plane (z/D=0).

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Figure 13

Development of Reynolds stress (⟨uw⟩/Us2) in the streamwise direction x/D for horizontal planes at (a) y/H=0.10, (b) y/H=0.51, and (c) y/H=0.76

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Figure 14

Three examples (a), (b), and (c) show coherent structures identified on the vertical central plane by the POD technique. The total kinetic energy recovered in these fields is ∼59.5% using the first six modes including mode 0.

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Figure 15

Examples of POD-reconstructed instantaneous velocity fields on the horizontal plane at vertical locations (a) y/H=0.10, (b) y/H=0.51, and (c) y/H=0.76. Each column shows three examples representing the velocity field at a specific vertical location. The total kinetic energy recovered was 90%, 86.7%, and 87.6%, respectively, using the first six modes including mode 0.

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