Turbulent Flow Structures and Scour Hole Characteristics around Circular Bridge Piers over Non-Uniform Sand Bed Channels with Downward Seepage

Chavan Chavan,Gualtieri Gualtieri,Kumar Kumar

doi:10.3390/w11081580

Chavan Chavan, Gualtieri Gualtieri + Show 1 more

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https://doi.org/10.3390/w11081580

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Abstract

In alluvial rivers bridge piers often cause local scour, a complex phenomenon as a result of the interaction between turbulent flow and bed material. In this paper, the results of an experimental study on the scour hole characteristics around single vertical pier sets on a non-uniform sand bed, under no seepage, and with downward seepage conditions, are described. In case of downward seepage, turbulent statistics, such as Reynolds stress, higher order moments, TKE-flux, and consequently sediment transport, decrease upstream of the pier, while increasing on both sides of it, where the enhanced erosive capacity of the flow results in an increase in the scour hole width. Moreover, the scour hole length shifts downstream. Empirical equations for the evaluation of scour hole characteristics, such as the length, width, area, and volume, including the downward seepage parameter, are proposed and experimentally tested. Model predictions give reasonably good agreement with the experimental data.

Highlights

Bridges play an important role in the transportation of goods and people across rivers
These results show the prevalence of a high turbulent activity, resulting in enhanced sediment transport, vertical profiles of the skewness factors in the streamwise (Su = u / u∗ ) and vertical (Sw = w /u∗ )
In order to deepen the impact of the downward seepage and the turbulent flow characteristics on the scour geometry around a pier, an experimental measurement of the instantaneous velocity with different percentages of with seepage (10% S and 15% S) and without seepage (NS) have been carried out in four different sections around a pier, for two different diameters (75 and 90 mm)

Summary

Introduction

Bridges play an important role in the transportation of goods and people across rivers. One of the most important issues is to protect bridge piers from collapse. Their foundation may be threatened by localized scour, as a result of the flow constriction of the cross-sectional area, and the subsequent increase of the flow velocity [1]. In order to ensure the protection of such structures, it is of a high priority to predict the flow field and sediment transport around the bridge piers. Melville and Coleman [5] stated that the flow field around a bridge pier is characterized by down-flow, surface roller, and wake vortices, such as the horseshoe vortex, at the base of the pier, and wake vortices behind the pier. The effect of the pier on flow separation, and the consequent sediment transport, depends on turbulence

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