Flow-induced vibration of a rotating circular cylinder at high reduced velocities and high rotation rates

Flow-induced vibration (FIV) of a rotating circular cylinder with high rotation rates between 4.5 and 8, a low Reynolds number (Re) of 100 and a mass ratio of 11.5 is investigated by two-dimensional numerical simulations. The responses of the high-speed rotating cylinder are classified into two steady flow regimes (S1 and S2), five vortex-induced vibration (VIV) regimes (VIV-1S, VIV-2S, VIV-T+S, VIV-2P and VIV-2P*) and two impulsive galloping (IG) regimes (IG and IG*). All the regimes are mapped on a rotation rate versus reduced velocity plane. In VIV-T+S regime, a triplex and a single vortex are shed alternatively from the cylinder in two consecutive vibration periods. VIV-2P* regime has the same number of vortices shed in each vibration period as VIV-2P, but the amplitude of vibration in two consecutive periods are different from each other. In all the identified VIV regimes, shear layers are separated from only one side of the cylinder and form vortices, instead of both sides which is observed at low rotation rates. This makes the flow patterns of all the identified VIV regimes different from the ones observed at low rotation rates. Impulsive galloping (IG) is the repetitive occurrence of the galloping peak followed by a few periods of VIV. Impulsive galloping occurs periodically in the IG regime and randomly in the IG* regime. During each IG period, the vibration displacement reaches an impulsive peak where the amplitude of vibration is increased significantly, followed by periodic oscillations of VIV.