Flow-induced vibration of a cylinder subjected to proximity interference by a downstream-cylinder

A numerical study is presented on flow-induced vibration of a circular cylinder, under the effect of a downstream stationary cylinder-induced proximity interference. The interference-induced various types of gap-flow regimes and characteristics of vibration and gap-flow rate $Q^*_g$ are presented, by considering various non-dimensional gaps $G^* = 0.1{-}2.5$ and reduced velocities $U^* = 3{-}20$ at a constant Reynolds number $Re = 100$ , mass ratio $m^*= 2$ and damping ratio $\zeta = 0.005$ . Decreasing $G^*$ or increasing proximity leads to the four gap-flow regimes: bi-directional gap flow at $G^* \geqslant 1.0$ , uni-directional non-orthogonal gap flow at $G^* = 1.5{-}1.0$ , uni-directional orthogonal gap flow at $G^* \leqslant 0.5$ and uni-directional one-sided gap flow at $G^* \leqslant 0.3$ . Further, the respective regimes at larger $U^*$ are associated with proximity-induced modified vortex-induced vibration (PImVIV), proximity-induced galloping (PIG), transitional PImVIV–PIG, and proximity-induced staggered vibration (PISV). Quantitative presentation of maximum gap-flow rate $Q^*_{{g,max}}$ , phase $ \phi _g$ (between $Q^*_{g}$ and displacement $y^*$ ) and phase portraits ( $Q^*_{g}$ versus $y^*$ ) provides clear demarcation between the various gap-flow regimes. Flow mechanisms are presented for the PImVIV, PIG and PISV responses. For the PIG, the mechanism is presented for the first time on generation of galloping instability, asymptotically increasing $A^*$ and existence of optimum gap $G^* = 0.5$ for the maximum amplitude. This work is significant as it provides new insights into the proximity interference-induced gap-flow dynamics between two cylinders, associated flow mechanism for both vibration mitigation and enhancement and promising potential applications for energy harvesting.