Divergent vibration of a test cylinder with a control cylinder at the rear

The objective of this study was to experimentally investigate flow-induced vibration occurring in a test cylinder capable of free vibration when there was a control cylinder with a diameter half of that of the test cylinder behind the test cylinder. This paper intensively investigated divergent vibration among flow-induced vibration characteristics of the test cylinder. The mechanism for generating divergent vibration was also determined. To clarify the mechanism, flow-induced vibration characteristics of the test cylinder and wakes were investigated when the control cylinder was located closely to the rear of the test cylinder. Among tests for investigating wakes, a visualization test was also conducted using hydrogen bubble as a dye in a water channel. As a result, it was found that when the control cylinder was in close proximity to the rear of the test cylinder, the divergent vibration that appeared in the test cylinder was divided into three patterns based on vibration amplitude characteristics. Results of wake investigation revealed that the presence of the control cylinder affected the emission frequency, shape, and intensity of the vortex discharged from the test cylinder, which in turn affected vibration characteristics of the test cylinder. As a result of investigating flow-induced vibration characteristics of the test cylinder using different methods by changing the flow velocity, vibration inertia was found to one cause for the divergent vibration of the cylinder.