The wake-induced vibration of a structure in the wake of another is investigated experimentally, using a rectangular cantilever cylinder having side ratio of 2. Dynamic responses are measured to investigate the effect of system parameters on the aerodynamic instability. The parameters include the free stream wind velocity and the position of the downstream cantilever cylinder in the wake generated by the upstream cylinder. The range of Reynolds numbers covered in this experiment is about $8×10^3$ - $3.5×10^4$. The wind velocity at which vortex shedding frequency coincides with the natural frequency of the downstream cantilever cylinder lies in this range.
In the uniform flow, galloping is founded to be the major mechanism for the vibration of the cantilever cylinder. In the wake, However, the cantilever cylinder vibrates with a large amplitude when the vortex shedding frequency coincides with the natural frequency of the cantilever cylinder. The vibration amplitude decreases notably as distance between two cylinders becomes large. No galloping phenomenon is observed when the cantilever cylinder is placed in the centerline of the wake generated by the upstream cylinder. As the cantilever cylinder keeps apart from the centerline, the cylinder gallops with smaller amplitude than in the uniform flow.