Flow pattern in the scour hole around a cylinder

Local scour around a bridge pier (cylinder) is a problem of much concern to hydraulic engineers. This is a complex phenomenon resulting from the interaction of the three-dimensional turbulent flow field around the cylinder and the mobile channel bed (see Fig. 1). In the vicinity of the cylinder, scouring is the consequence. In this paper, the three-dimensional flow field in an established (equilibrium) scour hole is experimentally investigated, An acoustic-Doppler velocity-profiler (ADVP) was used to measure instantaneously the three components of the velocities in the vertical symmetry (stagnation) plane of the flow before and after the cylinder. The vorticity of the flow field was calculated. Results of the study show, that a vortex-system is established in the front and a trailing wake-vortex system of strong turbulence is formed in the rear of the cylinder.