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Wake-induced galloping of two interfering circular cylinders

Published online by Cambridge University Press:  20 April 2006

A. Bokaian  and
F. Geoola
A. Bokaian
Affiliation:
Earl and Wright Ltd. Consulting Engineers, Victoria Station House, 191, Victoria Street London SW1E 5NE
F. Geoola
Affiliation:
Department of Civil Engineering, University College London, Gower Street, London WC1E 6BT
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Abstract

Measurements are presented of fluid-dynamic instability of a smooth circular cylinder, free to oscillate laterally against linear springs in the wake from an identical stationary neighbouring body. The observations also encompassed determination of static forces on the downstream cylinder as functions of relative position of the cylinder pair. Most of the experiments were performed under two conditions of free-stream turbulence. Static tests indicated that both the drag coefficient and the Strouhal number of the downstream body are continuous functions of its relative position. The drag forces were found to be negative at small gaps. It was observed that the transverse extent of the force field increases with increasing streamwise gap.

In the dynamic experiments, depending on the cylinders’ separation and structural damping, the cylinder exhibited a vortex-resonance, or a galloping, or a combined vortex-resonance and galloping, or a separated vortex-resonance and galloping. Whilst the characteristics of wake-excited motion were found to be essentially unaffected by a limited change in free-stream turbulence intensity, the galloping amplitudes were observed to be sensitive to the cylinders’ aspect ratio. An increase in the stability parameter caused significant effects on the cylinder response in amplitude domain. Wake observations behind the oscillating body indicated that in vortex lock-in the frequency of vortex-shedding locked to vibration frequency, but during small-amplitude galloping motion the shedding frequency behaved as if the cylinder was stationary.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 146 , September 1984 , pp. 383 - 415
Copyright
© 1984 Cambridge University Press

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