EXPERIMENTAL STUDY ON FLOW-INDUCED VIBRATION CONTROL OF MULTIPLE CYLINDERS IN TANDEM WITH HELICAL STRAKES

Flow-induced vibration (FIV) is a significant phenomenon that often occurs in actual situations, such as chemical towers, stacks, risers and offshore structures. Taking effective artificial measurements to control FIV is crucial to achieve the safe and long-period operation of engineering structures. Many researchers have verified that helical strakes can efficiently disturb the Karman vortex streets and suppress the vortex-induced vibration of isolated structures. The effect of helical strakes on controlling the FIV of gathered structures still needs to be investigated due to the complex vortex-structure interactions. A system of multiple cylinders with elastic support is an idealized representative to model the gathered engineering structures, which was used in the present work. The dynamic responses of three tandem cylinders (m*xi = 0.09) with helical strakes under different spaces were experimentally tested in a wind tunnel. All cylinders were allowed to vibrate in the cross-flow direction. The experimental wind speed range was 0.5 similar to 11 m/s, and the cross-section shapes of the helical strakes were designed to be square, involute and D-shaped. The vibration responses of the cylinders after installing helical strakes were analysed through comparison with those of the plain tandem cylinders. It is concluded that the D-shaped helical strake can decrease the FIV responses of tandem cylinders by 56.8% due to the reduction in the lift coefficients of the cylinders. Furthermore, the optimal parameters of the D-shaped helical strake for the tandem cylinders under different spaces were obtained, which can provide a theoretical basis for the FIV control of gathered engineering structures.