Flow-induced vibration of a cylinder attached with a fishtail-like fairing using wind tunnel experiments

Abstract

A flexible fishtail-like fairing, adopted as a flow-induced vibration(FIV) suppressor, was studied in a wind tunnel at Reynolds number 4000–42000. It is shown the vortex induced vibration can be practically eliminated by using FTF. The effect of the flexible plate length ratio, L/D (D is the diameter of the cylinder), and the fish hull angle, α, are investigated systematically. A fish hull with small α could extend the synchronisation range, but the effect is negligible with L prolonging. The response patterns and peak amplitudes of the cylinder are closely related to L, as well as the motion of the plate. VIV is found for L/D = 0.3–0.8, with mild deflection of the plate. FIV can be suppressed up to 94%–98% with L/D = 0.9–1.3. Flow visualization shows the nearfield vortex shedding is suppressed by the deflected plate. For L/D = 1.4–2.4, however, galloping-like instability is erupted when the vortex shedding frequency matches the 2fn (fn,the natural frequency of the system in air) harmonic component in the flow field together with the dramatic flapping of the plate. Besides, it seems that galloping-like response is sustained by the vortex shedding controlled by the motion of the flexible plate.