Numerical investigation for flow induced vibration from two oscillating cylinders

This study numerically investigates the flow-induced vibration characteristics of two tandem and side-by-side cylinders at Reynolds number of 100. The finite element method combined with the Arbitrary Lagrangian–Eulerian formulation is adopted to capture fluid–structure interaction behaviors. Numerical results reveal distinct flow regime transitions governed by spacing ratios. For tandem cylinders, the flow evolves sequentially from the extended-body regime and shear layer reattachment regime to the co-shedding regime as spacing increases. For side-by-side configurations, the flow transits from a single bluff-body pattern to a biased mode, eventually forming synchronized parallel vortex streets. For oscillating cylinders, strong near-field coupling dominates at small spacings, which weakens with increasing distance. When spacing exceeds critical thresholds (L/D≥4,H/D≥3), cylinder oscillation governs flow features, evolving into a weakly coupled state. Two mean phase differences based on the Hilbert transform are introduced to quantitatively characterize coupling strength, energy transfer, and vortex synchronization. Both spacing ratio and oscillation frequency (f0) jointly determine vortex patterns and lock-in phenomena. At the medium oscillation frequency (f0=0.160), stable lock-in behavior is well-established for small-spacing configurations. In contrast, at the low frequency (f0=0.080), tandem cylinders exhibit incomplete lock-in, whereas no lock-in phenomenon is observed for side-by-side counterparts. At the high frequency (f0=0.192), the lock-in effect fails for large-spacing configurations. These findings provide fundamental references for fatigue-resistant optimization of engineering structures.