Flow-induced vibration of two mechanically coupled pivoted circular cylinders: Vorticity dynamics

When both cylinders are at an equal distance from the pivot point, three major flow fields are observed. For larger gaps (g>3.9D), there is no reattachment of the shear layers downstream and two synchronized vortex streets form behind the two cylinders. By decreasing the gap, the downstream cylinder starts to interact with the vortexes shed from the upstream cylinder. If 2.5D < g < 3.9D, the gap flow pattern is split-gap where the vortexes split inside the gap before reaching the downstream cylinder. As the gap decreases, vortex excitation (VE) is less effective and gap-switching induced vibration (GSIV) dominates the vibration mechanism. Reducing the gap to G<0.9 turns the split-gap flow to an entire-gap flow pattern that forms a sharp velocity gradient inside the gap region and increases the total lift force dramatically on the system which maintains a larger vibration amplitude.