Vortex-induced vibration characteristics and aerodynamic interference of tandem 5:1 rectangular cylinders

Abstract

Wind tunnel tests and numerical simulations were conducted to investigate the vortex-induced vibration (VIV) characteristics and aerodynamic interference of tandem 5:1 rectangular cylinders. Influences of spacing ratio (L/B = 0.2, 1.0, and 3.0), constraint conditions, and damping ratio on VIV were systematically examined. Results reveal that the upstream cylinder (UC) dominates the VIV behavior of the tandem system. A freely vibrating UC excites large-amplitude VIV in the downstream cylinder (DC), up to three times that of an isolated cylinder, whereas a fixed UC almost eliminates DC vibration. The amplitude of DC depends nonlinearly on UC vibration under varying damping ratios, while the phase difference between the two cylinders varies systematically with both wind speed and damping ratio, reflecting the synchronization between vortex convection and structural vibration. The influence of DC on UC is confined to small and intermediate spacings and arises primarily from flow disturbance induced by proximity effects rather than by DC vibration. Flow-field analyses reveal distinct spacing-dependent interference mechanisms: at small spacing, UC vibration strengthens the leading-edge vortices of DC via vortex merging and gap cross flow; at large spacing, the periodic wake synchronized with UC vibration promotes strong leading-edge vortex shedding on DC. When the UC is fixed, the suppression mechanism also depends on spacing: at small spacing, a shielding effect suppresses leading-edge flow separation and vortex formation on DC; at large spacing, the Strouhal-frequency wake from the stationary UC prevents synchronization between DC shedding and structural vibration.