Experimental investigation of flow-induced vibration of a sinusoidally rotating circular?cylinder

摘要

The present experimental investigation characterises the dynamic response and wake structure of a sinusoidally rotating circular cylinder with a low mass ratio (defined as the ratio of the total oscillating mass to the displaced fluid mass) undergoing cross-stream flow-induced vibration (FIV). The study covers a wide parameter space spanning the forcing rotary oscillation frequency ratio $0leqslant f_{r}^{st }leqslant 4.5$ and the forcing rotation speed ratio $0leqslant unicode[STIX]{x1D6FC}_{r}^{st }leqslant 2.0$ , at reduced velocities associated with the vortex-induced vibration (VIV) upper and lower amplitude response branches. Here, $f_{r}^{st }=f_{r}/f_{nw}$ and $unicode[STIX]{x1D6FC}_{r}^{st }=unicode[STIX]{x1D6FA}_{o}D/(2U)$ , where $f_{r}$ is the forcing rotary oscillation frequency, $f_{nw}$ is the natural frequency of the system in quiescent fluid (water), $unicode[STIX]{x1D6FA}_{o}$ is the peak angular rotation speed, $D$ is the cylinder diameter and $U$ is the free-stream velocity; the reduced velocity is defined by $U^{st }=U/(,f_{nw}D)$ . The fluid–structure system was modelled using a low-friction air-bearing system in conjunction with a free-surface recirculating water channel, with axial rotary motion provided by a microstepping motor. The cylinder was allowed to vibrate with only one degree of freedom transverse to the oncoming free-stream flow. It was found that in specific ranges of $f_{r}^{st }$ , the body vibration frequency may deviate from that seen in the non-rotating case and lock onto the forcing rotary oscillation frequency or its one-third subharmonic. The former