Local Scour at Bridge Piers: The Role of Reynolds Number on Horseshoe Vortex Dynamics

This paper reports a comprehensive study of the major scour agent around bridge piers: the turbulent horseshoe vortex. The intricate and inherently unsteady characteristics of the junction flow are captured within a series of scaled laboratory experiments. We applied the state-of-the art Time-Resolved Digital Particle Image Velocimetry (TR-DPIV) technique to measure the velocity field at the centerline plane of symmetry upstream of a cylindrical model. Three levels of Reynolds numbers (Re D ) based on the obstacle diameter were studied: 26,000, 48,000 and 117,500. We evaluated the effect of this factor based on the time-averaged analyses of velocity and vorticity. Basic statistical analysis of the fluctuating velocity components provided insight to the physical mechanism that governs the behavior of the horseshoe vortex at the aforementioned levels of Re D .