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Fundamental Issues and Canonical Flows

# Characteristics of a Jet in the Vicinity of a Free Surface

[+] Author and Article Information
Jiahao Tian

Department of Mechanical, Automotive, and Materials Engineering,  University of Windsor, 401 Sunset Avenue, Windsor, Ontario N9B 3P4, Canada

Vesselina Roussinova

Department of Civil and Environmental Engineering,  University of Windsor, 401 Sunset Avenue, Windsor, Ontario N9B 3P4, Canadavtr@uwindsor.ca

Ram Balachandar

Department of Civil and Environmental Engineering,  University of Windsor, 401 Sunset Avenue, Windsor, Ontario N9B 3P4, Canadarambala@uwindsor.ca

J. Fluids Eng 134(3), 031204 (Mar 23, 2012) (12 pages) doi:10.1115/1.4005739 History: Received January 07, 2011; Revised November 27, 2011; Published March 20, 2012; Online March 23, 2012

## Abstract

In this study, the characteristics of a round turbulent jet in the vicinity of a free surface are investigated. The jet issued from a nozzle located at a depth five times the nozzle diameter (d = 10 mm) below and parallel to the free surface. The jet exit velocity was 2.8 m/s and the resulting Reynolds number was 28,000. Instantaneous two-dimensional PIV measurements were obtained in the vertical central plane and in several horizontal planes at various distances (y/d = 0,±1,±2,±3± 4) from the axis of the nozzle. All fields-of-view were positioned at streamwise locations in the range of 28 < x/d < 62, where the jet interacts significantly with the free surface. The results reveal that the behavior of the surface jet is very similar to that of the free jet before it interacts with the free surface which occurs at about x/d = 30. Beyond this, the velocity normal to the free surface is diminished and those parallel to the free surface are enhanced in the region near the free surface. In the horizontal plane near the free surface (y/d = +4), the spreading of the surface jet is significantly greater than that of the free jet. The mean lateral flow in this region tends to be outward everywhere for the surface jet, while the opposite trend occurs in the free jet. Turbulence intensities in all three directions are reduced by the effect of the free surface confinement. Near the free surface, at y/d = +4, unlike the single peak streamwise turbulence intensity profile noticed in the case of the free jet, the off-axis double peaks reappear in the case of the surface jet. The magnitude of shear stress in the vertical central plane of the surface jet is smaller than that noticed in the free jet near the free surface. In identical horizontal planes, the shear stress ($-uw¯$) profiles are similar in both free jets and surface jets in regions where the interaction with the free surface is not significant (x/d ≈ 30). As the downstream distance increases near the free surface, the magnitudes of the shear stress profiles are larger compared to that of the free jet. An increase in the normal component of vorticity is observed in the horizontal planes near the free surface.

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Copyright © 2012 by American Society of Mechanical Engineers
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## Figures

Figure 1

Schematic of the vertical plane (x-y) of the surface jet

Figure 2

Schematic of the experimental facility

Figure 3

Normalized mean axial velocity and turbulence intensity profiles at x/d = 0.2

Figure 4

Normalized mean axial velocity profiles for the free jet

Figure 5

Normalized mean streamwise (U/Uc ) velocity contour and vector profiles

Figure 6

Normalized mean streamwise (U/Uc ) velocity profiles on the (a) vertical central plane, and (b) horizontal central planes

Figure 7

Mean streamwise (U/Uc ) velocity profiles on the horizontal planes at x/d = 30, 45, and 60

Figure 8

(a) Normalized mean vertical (V/Uc ) velocity profiles in the vertical (x-y) central plane, and (b) normalized mean lateral (W/Uc ) velocity profiles in the horizontal (x-z) central plane

Figure 9

Contours of the mean lateral velocity (W) on various horizontal planes at y/d = 0 and ±4

Figure 10

Normalized mean streamwise (Urms /Uc ) turbulence intensity profiles in the (a) vertical (x-y) central plane, and (b) horizontal (x-z) central planes

Figure 11

Normalized streamwise (Urms /Uc ) turbulence intensity profiles in the horizontal planes at x/d = 30, 45, and 60

Figure 12

(a) Normalized vertical (Vrms /Uc ) turbulence intensity profiles on the vertical plane, and (b) normalized lateral (Wrms /Uc ) turbulence intensity profiles on the horizontal plane along the jet central plane at x/d = 30, 45, and 60

Figure 13

Normalized mean lateral (Wrms /Uc ) turbulence intensity profiles on the horizontal plane at x/d = 30, 45, and 60

Figure 14

(a) Streamwise development of the normalized Reynolds shear stress (uv¯  /Uc2) profiles on the vertical central plane and (b) streamwise development of the normalized Reynolds shear stress (uw¯  /Uc2) profiles on the horizontal central plane

Figure 15

Reynolds shear stress uw¯ (m2 /s2 ) contours for free jet (first column) and surface jet (second column) at y/d = 0, + 2, and + 4

Figure 16

Normalized mean Reynolds shear stress ()(uw¯  /Uc2)profiles on the horizontal planes (y/d = ±1, ±4) at x/d = 30, 45, and 60

Figure 17

Average vorticity ⟨Ωy⟩ contours at 30 < x/d < 42 on the horizontal planes (y/d = 0,+3) for free jet (first row) and surface jet (second row)

Figure 18

Average vorticity ⟨Ωy⟩ contours at 42 < x/d < 62 on the horizontal planes for free jet (first row) and surface jet (second and third row)

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