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Research Papers: Fundamental Issues and Canonical Flows

Manipulating Flow to Reduce Drag of a Square Cylinder by Using a Self-Sustained Vibrating Rod

[+] Author and Article Information
Rong Fung Huang1

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

Jeng Cha Cheng, Jia-Kun Chen, Ching Min Hsu

Department of Mechanical Engineering,  National Taiwan University of Science and Technology, Taipei, Taiwan 10672, Republic of China

1

Corresponding author.

J. Fluids Eng 133(5), 051202 (Jun 02, 2011) (14 pages) doi:10.1115/1.4004091 History: Received October 29, 2010; Revised April 21, 2011; Published June 02, 2011; Online June 02, 2011

The flow, vortex shedding, and surface pressure of a square cylinder at incidence were manipulated by means of a self-sustained vibrating rod placed around the leading edge of the upwind-facing lateral face of the square cylinder. The flow patterns on the cylinder surface were studied by using the surface-oil flow method for a Reynolds number between 4.5 × 104 and 1.1 × 105 as the incidence angle varied from 0° to 45°. Vortex-shedding characteristics were measured by means of a single-component hot-wire anemometer, and surface-pressure distributions were detected by using a linear-pressure scanner. The results show that owing to the influence of the rod vibration, the flow pattern on the agitated face changed from its natural state of a dual-ring bubble to the mode of boundary-layer separation. The critical incidence angle separating the dual-ring bubble and single-ring bubble modes was advanced to 11° from its natural state of 15°. The locations of the characteristic points on the cylinder surface were altered by the rod vibration, implying that the whole flow field surrounding the square cylinder was modified by the vibrating rod installed around the leading edge of the upwind-facing lateral face. The Strouhal numbers of wake instability of the controlled and uncontrolled cylinders did not present significant difference. The variations of the pressure coefficients induced by the rod vibration were closely related with the modification of the flow field on the cylinder surface. The decreases in the pressure coefficients on the upwind-facing faces and on the leeward-facing faces lead to drag reduction of the controlled cylinder by ∼25% when compared with the uncontrolled cylinder.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental setup. (a) Section view of square cylinder, (b) definitions of coordinates, surfaces of cylinder, and incidence angle.

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Figure 2

Surface-oil flow patterns on face B of square cylinder. Rew  = 7.7 × 104 , α = 0°. (a) no end plates, (b) end plates installed.

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Figure 3

Orbiting locus of rod vibration at Rew  = 7.7 × 104 . α = (a) 0°, (b) 18°, (c) 25°, (d) 36°.

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Figure 4

Surface-oil flow patterns of square cylinder under control of vibrating rod. Rew  = 7.7 × 104 . (a) face B, (b) face C, (c) face D.

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Figure 5

Two-dimensional topological flow patterns around square cylinder under control of vibrating rod. (a) dual-ring bubble regime (α < 11°), (b) single-ring bubble regime (11° < α < 45°), (c) wedge flow regime (α = 45°).

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Figure 6

Normalized locations of critical points on cylinder surfaces obtained by measuring surface-oil flow patterns. (a) face A, (b) face B, (c) face C, (d) face D.

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Figure 7

Data measured by hot-wire anemometer in cylinder wake at (x/w, y/w, z/w) = (3, 0.5, 0). (a) Instantaneous axial velocity, α = 13°, Rew  = 7.7 × 104 , (b) power spectrum density function, α = 13°, Rew  = 7.7 × 104 , (c) variation of vortex shedding frequency with incidence angle.

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Figure 8

Strouhal number based on projection width of cylinder on cross-stream plane

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Figure 9

Turbulence and wake width. (a) axial turbulence-intensity distribution along cross-stream direction measured at (x/w = 1, z/w = 0), α = 45°, Rew  = 7.7 × 104 , (b) variation of maximum turbulence intensity (which appears in shear layer) with incidence angle, (c) wake width.

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Figure 10

Distributions of pressure coefficients on surfaces of square cylinder under control of vibrating rod. α = (a) 0°, dual-ring bubble, (b) 25°, single-ring bubble, (c) 35°, single-ring bubble, (d) 45°, wedge flow. Shaded areas denote uncontrolled situation.

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Figure 11

Surface-averaged pressure coefficients of square cylinder in cross flow at Rew  = 6.2 × 104 . (a) face A, (b) face B, (c) face C, (d) face D.

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Figure 12

Aerodynamic performances of square cylinder in cross flow. (a) Drag coefficient, (b) lift coefficient.

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