Comparative study on a downstream cylinder versus splitter plate-based proximity interference on FIV of a circular cylinder

The study presents the effect of bluffness on flow-induced vibration of an elastically-mounted cylinder subjected to proximity-interference from a downstream stationary cylinder (bluff body) and a rigid splitter-plate (streamlined). Numerical simulations are performed for non-dimensional gap G* = 0 . 1,0.3, 0.5 and reduced velocities U* = 3 – 20, at a constant Reynolds number Re = 100. The upstream cylinder exhibits in-phase ( ϕ = 0°) proximity-induced galloping (PIG), except for an in-phase to anti-phase ( ϕ = 180°) jump at G* = 0.5 of the plate case, and the onset of proximity-induced staggered vibration (PISV) at U* = 20, G* = 0.1 of the cylinder case. With decreasing G* , the A* and maximum gap flow rate Q g , m a x * increases for the plate case while decreases for the cylinder, indicating a strong link between Q g , m a x * and vibrational amplitude. Three primary lift mechanisms are identified during PIG oscillation: anti-phase restoring vortex-induced lift, in-phase decelerating lift, and in-phase galloping lift. The persistence of the gap-side vortex and associated vortex-induced lift in the plate case, even at the smallest gap ( G* = 0.05)—contrasted with its suppression for the cylinder case, emerges as the fundamental difference between bluff and streamlined body interference. The well-known asymptotic amplitude variation (with U* ) of PIG is caused by the enhanced gap-side vortex, establishing the anti-phase restoring vortex as the key mechanism governing self-limiting amplitude characteristics in both PIG and VIV. Further, at G* = 0.1, the vibrational regime map is presented in terms of downstream structure bluffness B and U* .