Characterization of flow oblique to a circular cylinder with low aspect ratio using 3-D detached eddy simulation

Abstract

Large-amplitude vibrations of stay cables in cable-stayed bridges can threaten the safety and serviceability of the structures. Understanding of the excitation mechanism is necessary to mitigate such vibrations effectively and efficiently. Experimental research has investigated the mechanism of oscillation using flow oblique to a cylinder; however, since the aspect ratio of the cylinder is much lower than that of a real stay cable in bridges, the results might not reliably describe the real phenomenon. The aim of this study is (1) to provide better understanding of aspect ratio effects of a circular cylinder on aerodynamic characteristics of the cylinder oblique to flow associated with the large-amplitude cable vibrations and (2) to provide the experimentalists suggestions of a requisite aspect ratio and appropriate pressure-measuring positions of a cylinder for fully developed flow around the cylinder. To this end, the current work applied three-dimensional detached eddy simulations (DES) to flow around a yawed and inclined cylinder to investigate the importance of the aspect ratio of the cylinder when flow oblique to the cylinder develops fully along its spanwise axis. The Reynolds number is 1.4 × 10 5 based on the incoming flow velocity and the diameter of the cylinder. Three aspect ratios ( L/ D=10, 20, and 30; L: a cylinder length; D: a cylinder diameter) and two numerical conditions (slip and periodic) on spanwise boundaries were employed. Results showed that three-dimensional flow and the associated forces on a yawed and inclined cylinder are significantly influenced by the spanwise aspect ratios and spanwise boundary conditions. This study suggests that when a wind tunnel experiment investigates flow oblique to a very slender cylinder, such as attempting to model a stay cable, experimentalists should use a sufficiently high spanwise aspect ratio of the cylinder. For the case of the 30° yaw and 45° inclined cylinder, the requisite ratio would be approximately 60 or higher and appropriate pressure-measuring positions of a half to two-thirds of the cylinder length from its upper/upstream end in order to accurately model inherently three-dimensional characteristics of the flow.