On the coupling mechanism of rain-wind two-phase flow induced cable vibration: A wake-dynamics perspective

Abstract

Large amplitude rain-wind induced vibration (RWIV) of stay cables of long-span cable-stayed bridges has been a major concern in the past three decades, yet its excitation mechanism has not been clarified thoroughly. Recent numerical simulations and experimental work showed that when the RWIV of a cable is developing, the dominant frequency of its unsteady lift forces is notably decreased, i.e., the conventional Strouhal law of cylinder flow is obeyed. In some experimental studies, however, the small-scale vortical structures, which are believed to be closely associated with the low-frequency fluctuating components, are visualized qualitatively in the cable wake during the RWIV. In the present work, the first experimental observation of the dynamic wake behind a cable during the RWIV is presented. The RWIV is reappeared based on a stay cable model supported by springs in wind tunnel tests. The dynamic characteristics of the water rivulet on the upper surface of the cable are recorded by a high-speed camera, and the detailed wake flow of the cable is captured by employing the high-speed particle image velocimetry technique. We focus on the low-frequency synchronization between the cable vibration, upper-rivulet movement, and the wake dynamics to investigate the excitation mechanism of the RWIV. A three-phase (gas-liquid-solid) coupling scenario is finally proposed to explain this interesting phenomenon as low-frequency resonance between fluids and the cable structure.