Flow-induced vibration of a circular cylinder with an attached elastic plate of high aspect ratio
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abstract
The flow-induced transverse vibration of a cylinder (diameter D*) with an attached flexible and elastic plate of high aspect ratio to its leeward side is investigated numerically at a low Reynolds number of 150 for a range of reduced velocities (Ur) using an in-house developed fluid solver based on curvilinear immersed boundary method strongly coupled with an open-source finite element-based structural solver. It was observed that an attached elastic plate of width B=B*/D*=0.1 and length L=L*/D*=1 suppresses large vibrations of the cylinder, but one with length L=2, contrary to previous studies, amplifies vibrations up to five times of an isolated cylinder. Three regimes were observed: vortex-induced vibration (VIV), suppression, and galloping. In VIV regime for 3Ur7, lock-in was observed where the vortex shedding frequency from the plate-cylinder system was seen to slightly increase relative to that of static cylinderplate system to match with the natural frequency of the cylinder and the plate. In this regime, the deformations of the elastic plate were large (max. 91% of L) and in high modes (up to fifth mode), leading to new vortex patterns. The transverse displacement of the cylinderplate system was found to reach nearly twice of an isolated cylinder in this regime. For 7>Ur9, the cylinderplate system was pushed into suppression regime, wherein its displacement was nullified because of lack of vorticity interaction and out-of-phase deformation. Beyond Ur=9, the cylinderplate system vibrated in the galloping regime, wherein it shed and generated forces as an asymmetric body creating an angle of attack with the incoming flow. The primary mode of deformation of the elastic plate progressively increased from second mode to third mode in galloping regime, and the transverse displacement of cylinder showed a linear increase with the increase in reduced velocity until Ur=18. The vibration amplitude of the cylinder was higher in the galloping regime, but the vibrations of the plate were more intense (higher amplitude and mode) in the VIV regime. New vortex patterns were observed in the VIV and galloping regimes ranging from 2S mode till 2T mode including all the vortex pattern between them like 2S, 2P, 2Q, and P+T modes, which are reported for the first time.
