Abstract
Free vibration tests of a sphere tethered in a vertical water tunnel were conducted up to critical Reynolds number (3×10^5). The reduced velocity in the tests was in the range of 2〜36. Dynamic behaviors of a sphere were taken by a digital video camera. The drag force on the sphere was also measured. The sphere vibrates above a critical flow velocity, and circular or elliptical trajectories in the plane perpendicular to the flow direction can be observed. The relative amplitude increases as the flow velocity increases, and the sphere finally hits on the side wall of the water tunnel around the critical Reynolds number, i.e., the maximum amplitude of the vibration is beyond 2 times the sphere diameter.
