Wake-induced galloping of two interfering circular cylinders

Author:

Bokaian A.,Geoola F.

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.

Publisher

Cambridge University Press (CUP)

Subject

Mechanical Engineering,Mechanics of Materials,Condensed Matter Physics

Reference24 articles.

1. Yang, C. I. & Moran, T. J. 1979 Calculations of added mass and damping coefficients for hexagonal cylinders in a confined viscous fluid. In Flow-Induced Vibrations (ed. S. S. Chen & M. D. Bernstein ),pp.97–103.ASME.

2. Zdravkovich, M. M. 1977 Review of flow interference between two circular cylinders in various arrangements.Trans. ASME I: J. Fluids Engng 99,618–633.

3. Bokaian, A. & Geoola, F. 1984b Vortex-shedding from two interfering circular cylinders.Tech. Note, J. Engng Mech. Div., ASCE 110,623–628.

4. Zdravkovich, M. M. 1982 Flow-induced oscillation of two interfering circular cylinders. In Intl Conf. on Flow-Induced Vibrations in Fluid Engng, Reading, England ,pp.141–154.

5. King, R. & Johns, D. J. 1976 Wake interaction experiments with two flexible circular cylinders in flowing water.J. Sound Vib. 45,259–283.

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