Session: 08-06-02: VIV of Flexible Risers and Cables

Paper Number: 80115

80115 - Experimental Investigation of Flow Around a Single Circular Cylinder Freely Vibrating in Two Degrees-of-Freedom 

Abstract

Experimental investigations were performed for a single circular cantilevered cylinder located in a circulating water channel. The cylinder of mass ratio 1.78 and aspect ratio 17.8, vertically fixed at one end, was freely oscillating in the stream-wise and lateral directions. Reduced velocities of the flow past the cylinder, ranging from 0.65 to 5.85, corresponded to Reynolds numbers between 6.38 × 10³ and 5.65 × 10⁴.  At the inlet of the water channel, a Laser doppler velocimetry system measured stream-wise and span-wise flow velocity profiles. Corresponding turbulence intensities, cylinder accelerations and displacements, and forces acting on the single cylinder in the stream-wise and lateral directions were also measured. Vortex shedding frequencies were compared with cylinder response frequencies in the stream-wise and lateral directions for the cylinder. Coefficients of forces acting on the cylinder and their motion trajectories and accelerations were presented and analysed. The objective was to investigate the effect of relevant parameters for a cylinder oscillating in 2-DOF and to determine the universal wake Strouhal number for the cylinder and its comparison with the Strouhal number for a stationary cylinder. The universal Strouhal numbers, based on the vortex shedding frequencies, were compared with published data. Directly measured were cylinder accelerations, cylinder oscillations, and inertial forces acting on the cylinder and their trajectories of the downstream cylinder. The objective was also to directly obtain force coefficients from measurements. The stream-wise force coefficients turned out to be close to the coefficients for the stationary cylinder and, at higher Reynolds numbers, they increased. The resulting low uncertainties of measured values substantiated the reliability of our results. A particle image velocimetry (PIV) technique analyzed the wake’s flow topology, and a triaxial accelerometer measured the cylinder response. Wake patterns of shed vortices caused by the flow around the cylinder was experimentally investigated. The experiments provided reliable benchmark data suitable for numerical validation of vortex-induced vibration for circular cylinders oscillating in two degrees-of-freedom.

Key words: vortex-induced vibration, fluid-structure interaction, a single flexible cantilever circular cylinder, two degrees-of-freedom motions, universal Strouhal number, fluid forces.

Presenting Author: Hassan El Sheshtawy University of Duisburg-Essen (ISMT)

Authors:

Hassan El Sheshtawy University of Duisburg-Essen (ISMT)
Ould El Moctar University of Duisburg-Essen (ISMT)
Simon Tödter University of Duisburg-Essen (ISMT)
Thomas E. Schellin University of Duisburg-Essen (ISMT)