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CFD and VIV

Selective Roughness in the Boundary Layer to Suppress Flow-Induced Motions of Circular Cylinder at 30,000<Re<120,000

[+] Author and Article Information
Hongrae Park1

 Department of Mechanical Engineering, University of Michigan Ann Arbor, Michiganhrpark@umich.edu

Michael M. Bernitsas

 CTO of Vortex Hydro Energy,Department of Naval Architecture and Marine Engineeringand Department of Mechanical Engineering, University of Michigan Ann Arbor, Michiganmichaelb@umich.edu

R. Ajith Kumar2

 Department of Naval Architecture and Marine Engineering,University of Michigan Ann Arbor, MichiganRagajith@umich.edu

1

Corresponding author.

2

Present address: Amrita University, Amritapuri Campus, Kerala State, India.

J. Offshore Mech. Arct. Eng 134(4), 041801 (May 31, 2012) (7 pages) doi:10.1115/1.4006235 History: Received July 10, 2011; Revised January 31, 2012; Published May 30, 2012; Online May 31, 2012

A passive control means to suppress flow-induced motions (FIM) of a rigid circular cylinder in the TrSL3, high-lift, flow regime is formulated and tested experimentally. The developed method uses passive turbulence control (PTC) consisting of selectively located roughness on the cylinder surface with thickness about equal to the boundary layer thickness. The map of “PTC-to-FIM,” developed in previous work, revealed robust zones of weak suppression, strong suppression, hard galloping, and soft galloping. PTC has been used successfully to enhance FIM for hydrokinetic energy harnessing using the VIVACE Converter. PTC also revealed the potential to suppress FIM to various levels. The map is flow-direction dependent. In this paper, the “PTC-to-FIM” map is used to guide development of FIM suppression devices that are flow-direction independent and hardly affect cylinder geometry. Experiments are conducted in the Low Turbulence Free Surface Water Channel of the University of Michigan on a rigid, horizontal, circular cylinder, suspended on springs. Amplitude and frequency measurements and broad field-of-view visualization reveal complex flow structures and their relation to suppression. Several PTC designs are tested to understand the effect of PTC roughness, location, coverage, and configuration. Gradual modification of PTC parameters, leads to improved suppression and evolution of a design reducing the VIV synchronization range. Over a wide range of high reduced velocities, VIV is fully suppressed. The maximum amplitude occurring near the system’s natural frequency is reduced by about 63% compared to the maximum amplitude of the smooth cylinder.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 5

Effect of strip area converageon the cylinder response

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Figure 6

Map of roughness induced FIM showing Weak Suppression (WS), Hard Galloping (HG), Soft Galloping (SG), Strong Suppression (SS) response zones: (a) sand paper P180 and (b) sand paper P60

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Figure 7

Effect of helically wound roughness on the cylinder response

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Figure 8

Typical wake structures behind the cylinder with PTC configuration T7

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Figure 4

Effect of strip location on the cylinder response

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Figure 3

Effect of surface roughness on the cylinder response

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Figure 2

Photographers of cylinder with T7 (a) and T6 (b) PTC configurations

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Figure 1

Test cylinder mounted in the LTFSW channel: 1: 3.5″ cylinder, 2: side strut, 3: fixed shaft, 4: spring, 5: supporting bar, 6: supporter, 7: potentiometer, 8: linear bearing

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