Vortex-induced vibration of a bottom fixed flexible circular beam

Abstract

In this paper, we study the vortex-induced vibration of a bottom fixed circular cylinder with a 0.126 mass damping ratio and blockage ratio lower than 1%. The experiments were performed in a water tunnel at low Reynolds numbers (90<Re<350). The free end path of the cylinder was analyzed using a particle tracking velocimetry technique, while the shedding vortex modes were analyzed using a dye injection flow visualization technique. The results show a lock-in zone characterized by three recognizable regions which correspond to the: (1) initial, (2) upper and (3) lower branches. In the first region, the vortex-shedding can occur at different cylinder frequencies for a fixed Reynolds number. It is also observed that the combined fluid-cylinder response is dominated mainly by the natural frequency of the cylinder in still water and by the vortex-shedding frequency of a stationary cylinder. In the second region, the combined responses are dominated by the natural frequencies in both still water and still air. Finally, in the last region the vortex shedding and the cylinder frequency match very accurately with the natural frequency in still air.