Abstract
Visualization tests were performed to observe the wake and the vortices at 2nd unstable and stable regions. The test results showed that the distance between a vortices and the cylinder center was almost independent of the cylinder phase for a while. Then, when the phase of the cylinder was at 1/2π (downstream end of the oscillation) in the 2nd unstable region, the distance began to increase. The distance, however, began to increase at 0 in the stable region.
