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Research Papers: Fundamental Issues and Canonical Flows

Turbulent Features in the Coherent Central Region of a Plane Water Jet Issuing Into Quiescent Air

[+] Author and Article Information
Can Kang

Associate Professor
Mem. ASME
St. Anthony Falls Laboratory,
University of Minnesota,
Minneapolis, MN 55414
email: kangx603@umn.edu

Haixia Liu

Associate Professor
School of Material Science
and Engineering,
Jiangsu University,
Zhenjiang, Jiangsu 212013, China
e-mail: liuhx@mail.ujs.edu.cn

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received October 21, 2013; final manuscript received February 18, 2014; published online May 19, 2014. Assoc. Editor: Mark F. Tachie.

J. Fluids Eng 136(8), 081205 (May 19, 2014) (7 pages) Paper No: FE-13-1629; doi: 10.1115/1.4026924 History: Received October 21, 2013; Revised February 18, 2014

A plane water jet issuing into quiescent air at a Reynolds number of 2.5 × 105 is experimentally studied using phase Doppler anemometry (PDA). The plane water jet contains a coherent central region, which is situated immediately downstream of the nozzle exit. Particular emphasis is placed upon the distinctive attributes of such a region. Both mean flow pattern and turbulent features are obtained statistically based upon instantaneous velocity data. The central region is overwhelmingly dominated by uniformly distributed velocity, and remarkably high velocity gradient is present near the boundary of this region. Evidence shows that self-preservation is not satisfied in the central region. Explicit energy dissipation mechanisms in the central region are appreciated from cross-sectional uniform distributions of Kolmogorov length scales. Turbulent kinetic energy increases as the plane jet progresses, which is opposite to the general tendency associated with self-preservation. Although the central region is filled with near-zero Reynolds shear stress, distributions of skewness and flatness in this region are non-Gaussian and the instability caused by small-scale flow structures is thereby substantiated.

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Figures

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Fig. 1

Schematic view of a plane water jet issuing into quiescent air

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Fig. 2

Arrangements of PDA probes and monitored cross sections of the jet stream

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Fig. 3

Probability density of velocity at four sampling points. The time necessary for completing individual sampling processes is represented by tAm, tAe, tEm, and tEe, among which the first subscript denotes individual cross section and the second subscript denotes the position of the sampling point. For instance, tAm represents the time required for the complete sampling process at the midpoint on cross section A.

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Fig. 4

Two-dimensional velocity vectors and droplet diameters distributed on the five cross sections

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Fig. 5

Comparison of the decay of centerline velocity. The variation tendency of centerline velocity suggested by Browne et al. [14] is valid only when x/b ≥ 20; the variation tendency of centerline velocity suggested by Gordeyev and Thomas [15] is valid only when x/b > 10.

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Fig. 6

Comparison of semiwidth among three plane jets. The k = 0.104 line suggested by Browne et al. [14] corresponds to a plane jet with a Reynolds number of approximately 8000 and this line holds for x/b ≥ 20. The k = 0.109 line was suggested by Bradbury [5] and the corresponding Reynolds number is 3 × 104. The k = 0.109 line holds for x/b ≥ 30. The k = 0.577 line is the ideal jet edge fitting the diffusion angle of the plane nozzle used in the current study.

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Fig. 7

Variation of Kolmogorov length scale in the transverse direction

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Fig. 8

Distribution of relative turbulent kinetic energy on the five cross sections

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Fig. 9

Variation of Reynolds shear stress with normalized semiwidth

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Fig. 10

Skewness and flatness associated with the midpoints on the five cross sections

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