Two-Degree of Freedom VIV of a Circular Cylinder Pinned at One End

Abstract

This paper is a report on a study of vortex-induced-vibrations of a flexibly-mounted rigid circular cylinder immersed in a uniform free stream. This fluid-structure interaction experiment was carried out in the Rutgers Free-Surface Water Tunnel facility using a thin wall, 2.54 cm diameter, 109 cm long circular cylinder with a low mass-ratio. The cylinder was elastically mounted at its bottom end to the text section floor by a small diameter stainless steel pin. The top end of the cylinder was free to oscillate in both the cross-stream and streamwise directions. Extensive laser induced fluorescence flow visualization studies were carried out at the cylinder mid-height to investigate the response of the cylinder as well as the vortex shedding patterns. Flow visualization experiments were carried out over a Reynolds number range, based on cylinder diameter and free-stream speed, ranging from 820 to 6800. A range of vibration and vortex shedding modes were observed from these flow visualization studies. Symmetric vortex shedding was observed at low reduced velocities which evolved to ‘C’ shaped and ‘figure eight’ oscillations with increasing reduced velocity.