Effect of splitter plate length on FIV of circular cylinder

Abstract

The influence of the plate length on the flow-induced vibration (FIV) of a circular cylinder with a rigid splitter plate is numerically studied at a low Reynolds number of 100. The mass and damping ratios of the system are respectively m∗=10 and ζ=0. The reduced velocity (Vr) is varied from 2 to 26 and seven different nondimensional splitter plate length (L∗) values in the range of 0–2 are considered. Three different response patterns are identified in the present research, namely vortex-induced vibration (VIV), combined VIV-galloping and weak VIV-galloping. When the system is undergoing VIV, the frequency synchronisation is delayed and the lock-in range is enlarged with increasing L∗. The onset of galloping is postponed with the kink alleviated and the galloping frequency lowering. Abrupt drops in the vortex and total phases are associated with the initiation of galloping. In the galloping branch, both vortex and total forces remain in phase with the displacement. For the added mass and excitation coefficients (Cay and Cey) of the cylinder-plate assembly which have rarely been reported in the literature, Cay decreases as Vr is increased in the VIV range. Nevertheless, it leaps at the onset of galloping and the galloping response is accompanied by positive Cay values. Cey is negative in most cases and its trough appears at beginning of the VIV lock-in range or around the kink in the galloping branch. Due to the large-amplitude and low-frequency nature of the galloping oscillation, three new multi-vortex wake patterns (4P, 5P and 6P) are found to take place. Overall, for a longer splitter plate in the present study, the shear layer reattachment is observed at lower Vr and the galloping oscillation is associated with more vortex pairs.