Amplification of flow-induced vibrations of a circular cylinder by an oscillating minute attachment

The presence and circumferential oscillation of rivulets can excite large-amplitude vibrations for cables. Inspired by this phenomenon, a minute attachment was employed to simulate the upper-rivulet motion and successfully excited a large-amplitude vibration for a circular cylinder in a wind tunnel. By minute attachment, we mean a stainless-steel strip exhibiting morphological and dimensional characteristics analogous to the rivulet. The role of the circumferentially oscillating minute attachment on the flow-induced vibration of a circular cylinder was explored by detailed flow and structural measurements. The experimental results demonstrated that as wind velocity increased, the vibration amplitude of the model progressively increased, and the impact of the attachment on aerodynamics increased as well. It was also found that the wake behavior shifted from alternating vortex shedding to periodic "expansion-contraction" flapping in the boundary layers with increasing wind velocity. In particular, the oscillating minute attachment could control the boundary layer separation and form a "low velocity zone" on the upper surface of the model that varied with the attachment. Then, the aerodynamic lift force was synchronized with the attachment oscillation frequency, which was equal to the natural frequency of the vibrating circular cylinder. As a consequence, the vibration amplitude was rapidly developed.