Experimental investigation on flow-induced vibration of flexible multi cylinders in atmospheric boundary layer

Abstract

Experimental investigations of the flow-induced vibration (FIV) of flexible multi cylinders in tandem, side-by-side and staggered arrangements were conducted in an atmospheric boundary layer wind tunnel over a wide spacing ratio and incidence angles. All cylinders were cantilever supported and allowed to vibrate in cross-flow and inline directions. The vibration characteristics and transition features are identified among different configurations, and the responses dependent on reduced velocity under each configuration are discussed. Four regimes of the FIV of tandem cylinders are classified, where cylinder 1 vibrates divergently similar to galloping in Regime Ⅰ (l < 1.6, α = 0°) but is suppressed in Regime Ⅱ (1.6 ≤ l < 3, α = 0°), cylinder 2 always vibrates obviously in all four regimes, and cylinder 3 has a distinct vibration in only Regimes Ⅱ, Ⅲ (3 ≤ l ≤ 5, α = 0°) and Ⅳ (l >5, α = 0°), in which l is the nondimensional center-to-center distance and α is the incidence angle. There are two regimes for side-by-side cylinders, in which a divergent vibration of cylinder 1 is observed in Regime V (l < 1.6, α = 90°) and only cylinder 3 vibrates significantly in Regime VI (1.6 ≤ l ≤ 3.2, α = 90°). The aerodynamic properties analyzed through a prediction method are used to explain the vibration mechanism, in which the negative aerodynamic damping ratio branches sustain the divergent vibration in Regime I. Based on the comprehensive study above, the FIV phenomenon of flexible multi cylinders can be understood in atmospheric environment with nonuniform inflow, high turbulence intensity and subcritical Reynolds numbers. Finally, the potential of harvesting wind energy via this technique, showing the highest efficiency 52% but limited at Ur≥30, is discussed.