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Research Papers: Fundamental Issues and Canonical Flows

Statistical Properties of Round, Square, and Elliptic Jets at Low and Moderate Reynolds Numbers

[+] Author and Article Information
Seyed Sobhan Aleyasin

Department of Mechanical Engineering,
University of Manitoba,
Winnipeg, MB R3T 5 V6, Canada
e-mail: aleyasss@myumanitoba.ca

Mark Francis Tachie

Department of Mechanical Engineering,
University of Manitoba,
Winnipeg, MB R3T 5 V6, Canada

Mikhail Koupriyanov

Price Industries Limited,
Winnipeg, MB R2K 3Z9, Canada

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received February 10, 2017; final manuscript received May 7, 2017; published online July 21, 2017. Assoc. Editor: Pierre E. Sullivan.

J. Fluids Eng 139(10), 101206 (Jul 21, 2017) (11 pages) Paper No: FE-17-1087; doi: 10.1115/1.4036824 History: Received February 10, 2017; Revised May 07, 2017

An experimental study was conducted to investigate the effect of nozzle geometries on the statistical properties of free orifice jets at low and moderate Reynolds numbers. The studied cross sections were round, square, and ellipses with aspect ratios of 2 and 3. For each jet, detailed velocity measurements were made using a particle image velocimetry (PIV) system at Reynolds numbers of 2500 and 17,000. The results showed that at both Reynolds numbers, the elliptic jets had relatively higher velocity decay and jet spreading; however, the nozzle geometry effects were more pronounced at Re = 17,000 than at Re = 2500. Analysis of the swirling strength revealed that the rotational motions induced by vortices within the minor planes of the elliptic jets were stronger than observed in the major planes, square and round jets which were consistent with the relatively higher spreading observed in the minor planes. It was observed that the streamwise locations of the switchover points were independent of Reynolds number but are a strong function of aspect ratio. Based on the present results and those documented in the literature, a linear correlation was proposed for the location of axis-switching in orifice jets. Due to the axis-switching phenomena, a sign change was observed in the distribution of the Reynolds shear stress in the major planes of the elliptic jets. This results in the existence of regions with negative eddy viscosity in the near field regions, an observation that has an important implication for the predictive capabilities of standard eddy viscosity models.

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Figures

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Fig. 1

Schematic of experimental setup (not to scale)

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Fig. 2

Elliptic nozzle geometries: (a) ellipse2 and (b) ellipse3. The horizontal lines represent major axes while the vertical lines denote minor axes. All dimensions are in millimeter.

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Fig. 3

Contour plots of normalized mean streamwise velocity for (a) round, (b) ellipse2 in minor plane, and (c) ellipse2 in major plane at Re = 2500

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Fig. 4

Mean streamwise velocity decay on jet centerline at (a) Re = 2500 and (b) Re = 17,000

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Fig. 5

Development of half-velocity width at (a) Re = 2500 and (b) Re = 17,000

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Fig. 6

Streamwise locations of axis-switching points: elliptic orifice nozzles (: present_Re = 2500, : present_Re = 17,000, : Re = 8000 [13], : Re = 10,000 [28], : Re = 35,000 [13], : Re = 40,000 [17], : Re = 100,000 [16], Re = 188,000 [8], and : Re = 208,000 [29]), elliptic smooth contraction nozzles (: Re = 78,000 [9] and : Re = 100,000 [16]), rectangular orifice nozzles (: Re = 5400 [30], : Re = 8000 [13], : Re = 15,000 [31], : Re = 35,000 [13], : Re = 208,000 [14], and : [32]), and rectangular smooth contraction nozzles (:[33])

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Fig. 7

Evolution of the streamwise turbulence intensities on the jet centerline at Re = 2500

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Fig. 8

Contours of normalized instantaneous swirling strength for (a) minor and (b) major planes of ellipse2 at Re = 2500

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Fig. 9

Contour plots of normalized mean vorticity for (a) round and (b) minor and (c) major planes of ellipse2 at Re = 2500

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Fig. 10

Statistics of swirling strength (a) fraction of time with prograde, retrograde and nonzero swirling strength at Re = 2500, (b) average dimensionless swirling strength during prograde, retrograde and nonzero swirling events at Re = 2500, product of fraction of time and corresponding swirling at (c) Re = 2500 and (d) Re = 17,000. The profiles are extracted at x/d = 7. Symbols: round— prograde, retrograde, and nonzero; ellipse2_minor— prograde, retrograde, and nonzero; ellipse2_major— prograde, retrograde, and nonzero; square_prograde; and ellipse3_minor_prograde.

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Fig. 11

Normalized contour plots of Reynolds shear stress for ellipse3 in (a) minor and (b) major plane at Re = 17,000

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Fig. 12

(a) and (b) JPDF and (c) and (d) WJPDF contours of u and v for ellipse3_major at Re = 17,000. Plots are extracted at half-velocity width in the upper shear layer at (a) and (c) x/d = 1 and (b) and (d) x/d = 3.

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Fig. 13

(a) and (b) JPDF and (c) and (d) WJPDF contours of u and v for ellipse3_minor at Re = 17,000. Plots are extracted at half-velocity width in the upper shear layer at (a) and (c) x/d = 1 and (b) and (d) x/d = 3.

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Fig. 14

Eddy viscosity profiles at x/d = 1 at Re = 17,000

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