Aerodynamic forces induced by vertically oscillating incoming flow on a yawed horizontal circular cylinder

摘要

Large-amplitude vibrations of stay cables in cable-stayed bridges are an aeroelastic phenomenon caused by an interaction between wind and motion of the cables that is not yet fully explained. Understanding how flow around and the associated forces on an oscillating cable in the across-flow direction are developed interactively is essential to describe the mechanism of cable vibrations. This can ultimately lead to effective mitigation strategies for the large-amplitude vibrations. In this numerical study, using three-dimensional detached eddy simulation (DES), we considered vertically oscillating incoming flow over a stationary, yawed horizontal circular cylinder to investigate the effects of oscillation frequency on flow around and forces on the cylinder. The flow patterns and forces indicate that the incoming and around-cylinder oscillating flows interact significantly. Results showed that the flow around a yawed cylinder develops in different ways depending on the frequency of the incoming flow oscillation, resulting in changed characteristics of flow-induced forces. When incoming flow oscillated at frequencies similar to those of forces generated on the cylinder under uniform incoming flow, along-span flow that generated the low-frequency forces was intensified, i.e., the associated forces were strengthened while preserving their low frequency. However, when the incoming flow oscillated at a frequency close to that of Kármán vortex shedding, the along-span flow was suppressed while the Kármán vortex shedding phenomenon was strengthened over the whole cylinder length. This study suggests that when an oblique cable oscillates at a low frequency due to oblique wind-induced aerodynamic forces, those forces play an important role in initiating and increasing the vibration at the low frequency. A fluid-structure interaction analysis is planned that will shed more light on the phenomenon studied in this work by considering only the fluid motion.