The flow around bridge structures is a recent research topic, given the significance of bridges as basic engineering infrastructures. This study investigates the internal flow features around circular bridge piers by Particle Image Velocimetry applied both in the horizontal and vertical planes and therefore allowing for a quasi-spatial visualization of the velocity field. The temporal evolution of the vertical deflected flow at the pier front and the horseshoe vortex inside the increasing scour hole were explored resulting in the velocity and vorticity profiles. This work, therefore, provides novel insight into the complex and fascinating two-phase flow around circular bridge piers placed in loose sediment and provides an experimental data basis for advanced numerical simulation.
The temporal development of plunge pool scour was investigated using a novel experimental approach. Longitudinal profiles along the scour hole were recorded with an optical method to allow its definition at any time, from the initiation of scour to nearly the end-scour condition. The characteristics of the scour hole geometry were investigated, namely the maximum scour hole depth, the maximum ridge height, and their locations relative to the scour hole origin. It is demonstrated that the evolution is logarithmic, similar to that found for bridge pier and abutment scour. A distinction is further made between the developing and the developed scour hole phases. The main issue of the present research was to define the developed scour hole characteristics because the developing scour phase is influenced by turbulence features that may be difficult to assess. This work therefore allows for an appreciation of the temporal evolution of a scour process of engineering interest.
The effect of a single-peaked flood wave on pier scour is investigated both theoretically and experimentally. The conditions considered involve clear-water scour of a cohesionless material of given median sediment size and sediment nonuniformity, an approach flow characterized by a flow depth and velocity, a circular-shaped cylindrical bridge pier, and a flood hydrograph defined by its time to peak and peak discharge. A previously proposed formula for scour advance under a constant discharge was applied to the unsteady approach flow. The generalized temporal scour development along with the end scour depth are presented in terms of mainly the densimetric particle Froude number based on the maximum approach flow velocity and the median sediment size. The effect of the remaining parameters on the end scour depth is discussed and predictions are demonstrated to be essentially in agreement with model observations.
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