Explore generation mechanisms of unsteady large-amplitude wind-induced response in stay cables by delayed detached eddy simulation

The generation mechanisms of unsteady large-amplitude wind-induced vibrations in bridge stay cables under no precipitation condition are numerically studied through simulations of flow around a circular cylinder at an attack angle of α = 30° and Re = 10 4 . Delayed detached eddy simulation is performed in OpenFOAM 4.1 on a 4.1-million-cell O-type mesh to explore flow characteristics in the wake of a cylinder and the role of different vortical structures in triggering unstable aerodynamic responses. Results reveal that the axial flow formed on the leeward side of an inclined cylinder plays a key role in producing low-frequency excitations resulted from the intermittent interaction between axial vortex and conventional von Kármán vortex, leading to an intermittent amplification of von Kármán vortex shedding and thus the sectional lift. Such an intermittent intensification of sectional lift is found to propagate along the cylinder span at a speed matching the axial component of the oncoming flow velocity. Together, the intermittent amplification of von Kármán vortex shedding and the spanwise convection of enhanced sectional lift at the speed of axial flow introduces a marked low-frequency peak in the lift force spectrum. Further, the intensified sectional lift is observed to propagate along the cylinder span following an S-shaped wavy pattern. These identified unique features of flow around an inclined circular cylinder are believed to be the cause of the low-frequency component motion contained in the wind-induced unsteady responses of dry inclined stay cables reported from bridge sites and wind tunnel studies.