Aerodynamic performance of a grooved cylinder in flow conditions encountered by bridge stay cables in service

Abstract

Vibrations of dry bridge stay cables at relatively high wind velocities are of concern for a cable-stayed bridge. One approach to mitigate the vibrations is to modify the cross-sectional geometry of the cable and thereby its aerodynamic characteristics. Recent biological studies reveal that the cactus with a grooved cross-section can survive in high winds thanks to a less abrupt drag coefficient reduction with Reynolds number and a smaller fluctuating side force compared to a basic circular shape. This has inspired the attempt to take advantage of this natural evolution in the aerodynamic design of the protective sheath for bridge stay cables. This paper describes a series of wind tunnel tests on a cactus-shaped rigid cylinder consisting of eight ridges, eight troughs and with the groove depth-to-diameter ratio of 4%. It evaluates the static global aerodynamic forces under different yaw angles, angles of attack and segment rotations. The aerodynamic performance of the cactus cylinder is compared to a round cylinder from previous wind tunnel tests. The study aims to deepen the understanding of the particular groove effects in alleviating the wind excitation, and aid in the development of an alternative, aerodynamically efficient design of the protective sheath for stay cables.