Evolution and Turbulence Properties of Self-Sustained Transversely Oscillating Flow Induced by Fluidic Oscillator

[+] Author and Article Information
Rong Fung Huang1

 National Taiwan University of Science and Technology, Taipei, Taiwan 10672, Republic of Chinarfhuang@mail.ntust.edu

Kuo Tong Chang

 Mingchi University of Technology, Taipei, Taiwan 24306, Republic of China


Corresponding author.

J. Fluids Eng 129(8), 1038-1047 (Feb 03, 2007) (10 pages) doi:10.1115/1.2746905 History: Received April 04, 2006; Revised February 03, 2007

The evolution process and turbulence properties of a transversely oscillating flow induced by a fluidic oscillator are studied in a gravity-driven water tunnel. A planar jet is guided to impinge a specially designed crescent surface of a target blockage that is enclosed in a cavity of a fluidic oscillator. The geometric configuration of the cavity transforms the inherent stability characteristics of the jet from convective instability to absolute instability, so that the jet precedes the persistent back and forth swinging in the cavity. The swinging jet is subsequently directed through two passages and issued alternatively out of the fluidic oscillator. Two short plates are installed near the exits of the alternatively issuing pulsatile jets to deflect the jets toward the central axis. The deflected jets impinge with each other and form a pair of counter-rotating vortices in the near wake of the oscillator with a stagnation point at the impingement point. The stagnation point of the counter-rotating vortex pair moves back and forth transversely because of the phase difference existing between the two issued jets. The merged flow evolving from the counter-rotating vortices formed by the impingement of the two pulsatile jets therefore presents complex behavior of transverse oscillation. The topological models corresponding to the flow evolution are constructed to illustrate the oscillation process of the oscillating flow. Significant momentum dispersion and large turbulence intensity are induced by the transverse oscillation of the merged flow. The statistical turbulence properties show that the Lagrangian integral time and length scales of the turbulence eddies (the fine-scale structure) produced in the oscillating flow are drastically reduced.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Fluidic oscillator developed for inducing transversely oscillating flow

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Figure 2

Experimental setup

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Figure 3

Oscillation process of jet in cavity of fluidic oscillator. t*=t×Uj∕d, Red=1667, R∕d=4, h∕d=1.5. Framerate=60fps. Exposuretime=1∕60s.

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Figure 4

Instability domain of jet oscillation. Deflection plates not installed.

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Figure 5

Instantaneous flow visualization picture of fluidic oscillator. Deflection plates installed, deflection angle θ=60deg. Red=2000, R∕d=3.5, h∕d=2.5. Frame rate=60fps. Exposure time=1∕60s.

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Figure 6

Frequencies (a) and Strouhal numbers (b) of oscillating flow. Deflection plates installed. R∕d=3.5, h∕d=2.5.

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Figure 7

Hand sketches of topological flow evolution process

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Figure 8

Time-averaged velocity vector maps and streamline patterns (a, b, c) and corresponding vorticity contours (d, e, f) of oscillating flow. Deflection plates installed. Red=2000, R∕d=3.5, h∕d=2.5.

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Figure 9

Axial length of stagnation point of counter-rotating vortex pair. Red=2000, R∕d=3.5, h∕d=2.5.

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Figure 10

Time histories (a, b) and corresponding power spectrum density functions (c, d) of u and w velocity components. Deflection plates installed, deflection angle θ=60deg. Red=2000, R∕d=3.5, h∕d=2.5.

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Figure 11

Autocorrelation coefficients (a, b) and normalized Lagrangian time and length scales (c, d). Red=2000, R∕d=3.5, h∕d=2.5.

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Figure 12

Distributions of normalized velocity properties along central axis. (a) axial velocity, (b) axial turbulence intensities, (c) lateral turbulence intensity. Red=2000, R∕d=3.5, h∕d=2.5.




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