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Selective roughness in the boundary layer to suppress flow-induced motions of circular cylinder at 30,000Re120,000

Publisher : Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE

Year : 2011, 2012

Abstract : ? 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 method developed 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. The same technology 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 flowdirection 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 PTC direction, roughness, thickness, and coverage. Gradual modification of PTC parameters, leads to improved suppression and evolution of a design reducing the VIV synchronization range, fully suppressing VIV in a wide range, and reducing the maximum occurring near the system's natural frequency by about 60% compared to the maximum amplitude of the smooth cylinder. Copyright © 2011 by ASME.

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