Abstract
The mechanism of the vortex induced vibration of a circular cylinder was discussed based on numerical simulations of the discrete vortex model. The cylinder vibrates even when the frequecy of the vortex shedding is not locked in that of the vibration. Because the vortex sheds into the wake synchronized with the vibration in a regular interval and encourages the vibration in the interval. The process to the lock-in state is triggered by the prevention of the rolling up of the shear layer by the vibration. Therefore, the lock-in phenomenon can be considered as the transition from the vortex shedding by the interaction of the shear layers to the one controlled by the vibration. When the splitter plate is set in the wake, the interaction of the shear layers is prevented and the lock-in state can be occurred in the wider range of flow velocity. As the result, the cylinder can vibrate even in very high velocity.
