Research Papers: Fundamental Issues and Canonical Flows

Experimental Investigation of Nozzle Spacing Effects on Characteristics of Round Twin Free Jets

[+] Author and Article Information
Andrew Laban

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

Seyed Sobhan Aleyasin

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

Mark Francis Tachie

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

Mike Koupriyanov

Price Industries Limited,
Winnipeg, MB R2K 3Z9, Canada
e-mail: mikek@priceindustries.com

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received April 13, 2018; final manuscript received November 11, 2018; published online January 7, 2019. Assoc. Editor: Philipp Epple.

J. Fluids Eng 141(7), 071201 (Jan 07, 2019) (11 pages) Paper No: FE-18-1263; doi: 10.1115/1.4041989 History: Received April 13, 2018; Revised November 11, 2018

The objective of this paper is to investigate the effects of nozzle spacing on the mean velocity and higher-order turbulent statistics of free twin round jets produced from sharp contraction nozzles. The experiments were performed in an air chamber where four nozzle spacing ratios, S/d = 2.8, 4.1, 5.5, and 7.1, were investigated at a fixed Reynolds number of 10,000. A planar particle image velocimetry (PIV) system was used to conduct the velocity measurements. The results show that downstream of the potential core, a reduction in spacing ratio leads to an earlier and more intense interaction between the jets, indicated by enhanced half-velocity width spread rate in the inner shear layers and a significant rise of turbulent intensities and vorticity thickness along the symmetry plane. A reduction in spacing ratio, however, confines the ambient fluid entrainment along the inner shear layers leading to a reduced core jet velocity decay rate. The closer proximity of the jets also leads to the decrease of Reynolds stresses in the inner shear layers but not in the outer shear layers. The Reynolds stress ratios along the jet centerline reveal the highest anisotropy in the potential core region.

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Fig. 1

Schematic of twin jet configuration

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Fig. 2

(a) Schematic of test facility and (b) test round nozzle with a modified contraction. All units in millimeter.

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Fig. 3

Contours of normalized streamwise mean velocity, U/Umax, and spanwise vorticity, Ωz×d/Umax, for ((a), (c)) S/d = 2.8 and ((b), (d)) S/d = 7.1

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Fig. 4

(a) Evolution of normalized streamwise mean velocity along the centerline and symmetry line, (b) merging point, (c) combining points, and (d) normalized streamwise mean velocity along the symmetry line

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Fig. 5

(a) Jet centerline velocity decay, (b) outer shear layer half-velocity width, (c) inner shear layer half-velocity width, and (d) local vorticity thickness along the jet's inner shear layer

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Fig. 6

One-dimensional profiles of normalized streamwise mean velocity at selected locations for S/d = 2.8, 4.1, and 7.1

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Fig. 7

Contours of normalized Reynolds shear stress, uv¯/Umax2, streamwise normal stresses, u2¯/Umax2, and transverse normal stresses, v2¯/Umax2, for ((a), (c), (e)) S/d = 2.8 and ((b), (d), (f)) S/d = 7.1

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Fig. 8

Development of (a) urms/Umax and (b) vrms/Umax along the symmetry plane and jet centerline; development of (c) urms/Ucl and (d) vrms/Ucl along the jet centerline; and scaling of (e) urms and (f) vrms along the symmetry plane

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Fig. 9

Reynolds normal stresses ratio along jet centerline

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Fig. 10

One-dimensional profiles of normalized (a) Reynolds shear stresses, (b) streamwise normal stresses, and (c) transverse normal stresses at selected locations for S/d = 2.8, 4.1, and7.1

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Fig. 11

Contours of normalized turbulent kinetic energy, (k/Umax2), production, (Pk×d/Umax3), convection, (Ck×d/Umax3), and turbulent diffusion, (Dk×d/Umax3), for ((a), (c), (e), (g)) S/d = 2.8 and ((b), (d), (f), (h)) S/d = 7.1



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