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TECHNICAL PAPERS

Influence of Reynolds Number on the Evolution of a Plane Air Jet Issuing From a Slit

[+] Author and Article Information
P. R. Suresh, T. Sundararajan

Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, India

Sarit K. Das

Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, Indiasariṯdas@hotmail.com

J. Fluids Eng 129(10), 1288-1296 (May 17, 2007) (9 pages) doi:10.1115/1.2776959 History: Received November 22, 2005; Revised May 17, 2007

Jet flows are encountered in a variety of industrial applications. Although from the points of view of manufacturing with ease and small spatial requirement it is convenient to use short slit nozzles, most of the available studies deal with turbulent jets issuing from contoured nozzles. In the present work, experiments have been conducted in the moderate Reynolds number range of 250–6250 for a slit jet. Mixing characteristics of slit jets seem to be quite different from those of jets emerging out of contoured nozzles. This is primarily due to the differences in the decay characteristics and the large scale eddy structures generated in the near field, which are functions of the initial momentum thickness. It is evident that, in the range of 250Re6250, the overall spreading characteristics of the slit jet flow have stronger Reynolds number dependence than those of contoured nozzle jets. In particular, the slit jets exhibit slower mean velocity decay rates and slower half-width growth rates. Normalized power spectra and probability distribution functions are used to assess the spatial evolution and the Reynolds number dependence of jet turbulence. It is seen that the fluctuating components of velocity attain isotropic conditions at a smaller axial distance from the nozzle exit than that required for mean velocity components to become self-similar.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the experimental setup

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Figure 2

Mean and rms velocity variation across the jet cross section. Note: Solid symbols represent axial velocity and open symbols represent turbulence intensity.

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Figure 3

(a) Development of mean velocity in the near field. Note: N&O represents Ref. 8. (b) Inverse of the mean square velocity decay. N&O represents Ref. 8.

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Figure 4

(a) Axial evolution of turbulence intensity (u∕Uc). (b) Axial evolution of fluctuating velocity components for Re=2000. (c) Axial evolution of fluctuating velocity components for Re=6250.

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Figure 5

Spectral variation of velocity fluctuations along the axis for Re=550

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Figure 6

Spectral variation of velocity fluctuations along the axis for Re=1100

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Figure 7

Spectral variation of velocity fluctuations along the axis for Re=6250

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Figure 8

Variation of St along the centerline and shear layer for Re=1100 and Re=6250

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Figure 9

(a) Reynolds number dependence of PDF in the near field (x∕d=10). (b) Reynolds number dependence of PDF in the far field (x∕d=80). (c) Reynolds number dependence of PDF in the very far field (x∕d=140).

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Figure 10

Variation of wave number spectrum along the axis for Re=6250

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Figure 11

Reynolds number dependence of wave number spectrum at x∕d=80

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Figure 12

Variation of integral length scale along the axis

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Figure 13

Reynolds number effect on turbulent dissipation ε

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Figure 14

Effect of Reynolds number on jet half-width variation. Note: N&O represents Ref. 8.

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