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Research Papers: Fundamental Issues and Canonical Flows

Coherent Streamwise Vortex Structures in the Near-Field of the Three-Dimensional Wall Jet

[+] Author and Article Information
Lhendup Namgyal

e-mail: namgyaling@gmail.com

Joseph W. Hall

e-mail: jwhall@unb.ca
Department of Mechanical Engineering,
University of New Brunswick,
Fredericton, NB, E3B 5A3, Canada

The term near-wall vorticity refers to the regions of streamwise vorticity that are close to the wall, but should not be considered to truly be in the “near-wall region,” as the measurements are not adequate to resolve this area.

1Corresponding author.

Manuscript received May 24, 2012; final manuscript received February 22, 2013; published online April 12, 2013. Assoc. Editor: Mark F. Tachie.

J. Fluids Eng 135(6), 061204 (Apr 12, 2013) (7 pages) Paper No: FE-12-1260; doi: 10.1115/1.4023855 History: Received May 24, 2012; Revised February 22, 2013

A turbulent three-dimensional wall jet with an exit Reynolds number of 250,000 was investigated using stereoscopic particle image velocimetry (PIV) in the near-field region (x/D = 5). The proper orthogonal decomposition (POD) was applied to all three components of the velocity field to investigate the underlying coherent structures in the flow. A low-dimensional reconstruction of the turbulent velocity field using the first five POD modes showed the presence of coherent streamwise vortex structures formed in the outer shear-layers of the wall jet, not unlike those found in the near-field of free jets. The instantaneous streamwise vorticity reconstructed from the low-dimensional reconstructed velocity field indicates the presence of a persistent vortex pair close to the wall and on either side of the jet centerline that appear similar to the mean streamwise vorticity. These regions do not appear to be directly related to the positioning of the streamwise vortex structures in the outer shear-layer.

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Figures

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Fig. 1

(a) Schematic of a three-dimensional wall jet issuing from a contoured nozzle and (b) experimental setup showing laser and PIV camera arrangement

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Fig. 2

Contours of the (a) mean streamwise velocity, (b) mean normal velocity, (c) mean lateral velocity, and (d) mean streamwise vorticity

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Fig. 3

(a) Turbulent energy distribution in the first 39 modes, and (b) first, (c) second, (d) third, (e) fourth, and (f) fifth POD mode shape

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Fig. 4

Contours and vectors plot of the instantaneous velocity at a random instant, (a) actual U, (b) reconstructed U using first five POD modes, (c) actual V & W, and (d) reconstructed V & W using first five POD modes

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Fig. 5

POD reconstruction of the instantaneous velocity using first five POD modes and instantaneous streamwise vorticity

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Fig. 6

Proposed coherent structure model in the near-field of the turbulent three-dimensional wall jet exiting from a contoured nozzle

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