This study is concerned with flow-induced vibration phenomena in multiple objects. The vortex formation during the onset of unstable vibration in wake galloping in a square prism is investigated. The upstream fixed object and the downstream vibrating object are both square prisms, and the downstream object is installed in forced vibration experiments. The experiment was conducted in a water channel, and the unstable vibration conditions of a wind tunnel free-vibration experiments were reproduced by using the arrangement of the two prisms, the reduced velocity, and the amplitude of the downstream vibrating object as parameters. The results of the experiments showed that an increase in vibration displacement resulted in a flow pattern comprising one flow cycle per two vibration cycles. On the other hand, the vibration displacement decreased, the flow was a flow with a cycle in which the vortex formed when the vibration displacement of the vibrating object was large was disrupted. Also, the relationship between amplitude changes and flow pattern was clarified.
YADA et al. (Wed,) studied this question.