Flow control and vibration response of a circular cylinder attached with a wavy plate

Flow past a circular cylinder fitted with a rear rigid wavy plate at a low Reynolds number of Re = 150 is first numerically studied in this work. The effects of the plate length and the surface undulation on the hydrodynamic forces and vortex shedding behavior of the circular cylinder are examined. The mean drag coefficient and the fluctuation of lift coefficient are reduced up to 27.5% and 54.9%, respectively, in the presence of a wavy plate. Additionally, the vortex formation length is elongated and the wake width is shortened, illustrating the suppression of vortex shedding. According to the flow control performance, the 1.5D-length (D is the cylinder diameter) wavy plate with wavelength of 3D is employed to control the vortex-induced vibration (VIV). The twodegree-of-freedom of flow-induced vibration is computed for a wide range of reduced velocities (U-r = 2-20) in comparison with a bare cylinder. The results indicate the initial and lower branches of VIV are effectively suppressed by the wavy plate with the maximum reduction of cross-flow amplitude up to 92.44%. Nevertheless, the reattachment of shear layers on the wavy plate surface and the asymmetric P + S (a single vortex and a pair of opposite signed vortices released per cycle of shedding) vortex structure stir the galloping instability at U-r > 8, instead of the desynchronization branch. The monotonic increase of vibration amplitude in galloping branch shows a greater potential for energy harvesting.