Explore Essential Elements in the Generation Mechanisms of Wind-Induced Cable Vibrations: An Insight Offered by Numerical Techniques

Abstract

The inclined and/or yawed orientation of bridge stay cables results in the formation of secondary axial flow on the leeward side of cable surface, the intensity of which depends on the effective attack angle. On the other hand, the cross-sectional shape of a real stay cable is usually not perfectly round. It is believed that the presence of axial flow and roundness imperfection would contribute to trigger some unique wind-induced cable vibration phenomena. To clarify their respective role in the excitation mechanisms, a delayed detached eddy simulation (DDES) is performed in OpenFOAM on an inclined circular cylinder. The effect of cable orientation is studied for $\alpha \, = \,0^\circ ,{ 3}0^\circ ,{ 45}^\circ ,{ 6}0^\circ$ at ${\text{Re}}\, = \,{1}.0\, \times \,{1}0^{{4}}$ and ${1}.{4}\, \times \,{1}0^{{4}}$, whereas the impact of cable cross-sectional shape is examined for four different levels of roundness imperfection. Results show that the interaction between Kármán vortex and axial vortex causes an “S” pattern movement of a low C_p region along cable leeward surface, which generated an intermittently amplified transverse lift. This could be the source which triggers unstable cable motion. Further, the strength of axial flow is found critical to its interaction with Kármán vortex. This explains why aerodynamic instability of a cable was only observed at certain cable orientations in lab and on site. In addition, an imperfectly round cable is observed to have a smaller recirculation region in the wake, which helps to trap more axial flow close to the cable leeward surface and may enhance the interaction between axial and Kármán vortices.