Dynamic response of a circular cylinder in the presence of a detached splitter plate: On the gap distance sensitivity

Flow-induced vibration of a circular cylinder fitted with a detached rear splitter plate in a laminar flow with Re = 120 is studied numerically. Effects of the gap distance (G/D = 0-2) and reduced velocity (Ur = 2-18) on the vibration response, flow pattern, and hydrodynamic coefficient are investigated in detail. As the gap distance increases, three vibration responses are identified: IB-resonance-galloping at G/D = 0, VIV with a wide lock-in region but low frequencies at G/D = 0.5 and 1, and typical VIV at G/D = 1.5 and 2. The associated phase difference angles and the added mass coefficients for the VIV responses at G/D = 0.5-2 show a jump from 0 degrees to 180 degrees and a transition from positive to negative, respectively, while they always keep being zero and positive for the IB-resonance-galloping response at G/D = 0. At G/D = 0-1, the shear layers from the cylinder surface cannot roll up to form complete vortices in the cylinder wake but reattach to the splitter plate's surface or rear tip, leading to the overshoot (OS) and shear-layer reattachment (SR) flow pattern, and meanwhile the elongated vortex formation length and delayed vortex shedding. As a consequence, the optimal drag-and lift-reductions are achieved at G/D = 1. In contrast, complete vortices can be found both behind the cylinder and plate for the cases of G/D = 1.5-2, resulting in the co-shedding (CS) flow pattern, including CS-I and CS-II pattern based on whether the vortices from the cylinder and plate are merged or not. The 2S vortex shedding modes are generally observed at present Reynolds number, while the 2P modes are identified in the galloping and lock-in region. The splitter plate positively contributes to the total lift forces when the cylinder-plate body gallops, while it presents a negative effect by counteracting the forces on the plate itself or on the circular cylinder in the VIV region. (c) 2023 Elsevier Ltd. All rights reserved.