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Research Papers: Fundamental Issues and Canonical Flows

Characteristics of Flow Structures in the Wake of a Bed-Mounted Bluff Body in Shallow Open Channels

[+] Author and Article Information
G. Nasif, R. M. Barron

Department of Mechanical, Automotive
and Materials Engineering,
University of Windsor,
Windsor, ON N9B 3P4, Canada

R. Balachandar

Department of Mechanical, Automotive
and Materials Engineering,
University of Windsor,
Windsor, ON N9B 3P4, Canada
e-mail: rambala@uwindsor.ca

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received January 21, 2015; final manuscript received May 1, 2015; published online June 15, 2015. Assoc. Editor: Alfredo Soldati.

J. Fluids Eng 137(10), 101207 (Oct 01, 2015) (10 pages) Paper No: FE-15-1049; doi: 10.1115/1.4030537 History: Received January 21, 2015; Revised May 01, 2015; Online June 15, 2015

The characteristics of the flow structures observed in the wake of a bluff body mounted vertically on the bed and normal to the flow in a shallow open channel are investigated using detached eddy simulation (DES). The flow structures in the shallow wake are identified using the λ2-criterion. A distinctive feature in the time-averaged flow field, referred to as the owl face of the first kind, is observed. The position of this spiraling structure is stable at locations close to the bed, while its rotation sense switches from stable inward to unstable outward spiraling as it moves toward the free surface, where the bed friction becomes insignificant and the flow develops into a traditional two-dimensional (2D) wake. A three-dimensional (3D) structure resulting from a horizontally oriented secondary roll-up process is observed immediately downstream of the base of the bluff body in the center of the near-wake region. In addition to the horseshoe vortex, a new structure that wraps around the bluff body in the toe region is identified, referred to as a collar vortex. The presence of the coherent structures in the near-bed region is highlighted and their influence on the wake region is discussed.

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References

Figures

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Fig. 1

Schematic of the flow (adapted from Ref. [11])

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Fig. 2

Development of (a) streamwise and (b) transverse, root-mean-square velocity at downstream location X/D = 1.0 on the horizontal plane Y/H = 0.50

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Fig. 3

λ2 isosurface shaded by vorticity vector components: (a) Y-vorticity, (b) X-vorticity, and (c) Z-vorticity at (t/T ≈ 0.5)

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Fig. 4

Vorticity magnitude on the vertical planes X/D = 0.1, 0.3, 0.5, and 1.0 at (t/T ≈ 0.5)

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Fig. 5

Time-averaged streamtraces of the velocity shaded by vorticity magnitude on the vertical plane Z/D = 0.0

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Fig. 6

Streamtraces of the time-averaged velocity superimposed with the contours of time-averaged vorticity magnitude at different horizontal planes from the bed

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Fig. 7

Streamtraces of time-averaged velocity superimposed with the contours of time-averaged vorticity magnitude at different vertical planes from the bluff body

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