We numerically study the rotational flow-induced vibrations (FIV) of an inverted cylinder-plate, consisting of a rigid circular cylinder and an attached splitter plate on its windward side. A torsional spring mounted at the center of the cylinder facilitates a one degree-of-freedom flow-induced rotational motion. While splitter plates are conventionally utilized to suppress the vibrations of bluff bodies, the present study demonstrates the opposite effect of enhancing the vibrations. We employ an in-house, sharp-interface immersed-boundary-method-based flow solver, which is one-way coupled to a forced torsional harmonic oscillator equation. Our two-dimensional simulations at a Reynolds number of 100 show the existence of several FIV regimes as a function of reduced velocity, namely, initial excitation, intermediate and final symmetry breaking, large-amplitude oscillations, and chaos. We demonstrate the presence of harmonic lock-in during large-amplitude oscillations through frequency synchronization and enhanced energy exchange between structure and fluid. Leading-edge vortices (LEVs) form during the large-amplitude oscillation and symmetry-breaking regimes and create large negative pressure zones that drive the cylinder-plate to undergo significant displacements. The splitter plate length influences the LEV formation and the strength of LEVs diminishes for shorter plates, resulting in a significant drop in amplitude. As the structure-to-fluid density ratio increases, the range of reduced velocity over which the regimes are observed becomes broader. Synchronized oscillations of the cylinder-plate with fluid forcing indicate vortex-induced vibrations as the driving mechanism. This is further confirmed through dynamic mode decomposition of the vorticity field, which reveals that the dominant vortex-shedding mode remains synchronized with the cylinder-plate oscillations across the regimes.

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• Flow-structure interactions
• Vortex dynamics
• Immersed boundary methods