Flow-induced vibrations of two staggered cylinders with a moderate spacing and varying incident angles at subcritical Reynolds numbers

Abstract

Two-degree-of-freedom (2DOF) flow-induced vibrations (FIV) of a stagger-arranged circular cylinder pair with a constant centre-to-centre spacing ratio P/D=6.0 and varying incident angles (α) are numerically studied. The two cylinders can oscillate freely in both the in-line and cross-flow directions. The Reynolds number range Re=1470–10320 belongs to the subcritical flow regime. Two identical cylinders with mass ratios of m∗=2.6 and mass-damping parameters of m∗+Caζ=0.013 are adopted in the present simulation. Four incident angles ranging from 0° to 90° with an increment of 30° are considered to investigate the effect of α on the FIV responses, hydrodynamic characteristics and wake patterns of the two cylinders at this specific P/D. For small incident angles (i.e., α=0° and 30°), the influence of Cylinder II on the FIV of Cylinder I is almost negligible. In contrast, owing to the complicated wake–cylinder and wake–wake interactions, large-amplitude vibrations are found for Cylinder II at high reduced velocities (Vr). The wake patterns suggest that the periodic vortex coupling arisen from the synchronous movements between the upstream vortices and Cylinder II contributes to maintaining a vibration mode that resembles wake-induced flutter (WIF). For large incident angles of α=60° and 90°, the two cylinders oscillate similarly and their response amplitudes experience decline at lower Vr values. The analyses of the wake characteristics demonstrate that the restrained wake widths and the stronger proximity interference between the two cylinders lead to the vibration attenuation.