Hydrodynamic Structure with Scour Hole Downstream of Bed Sills

Mouldi Ben Meftah,Michele Mossa,Diana De Padova,Francesca De Serio

doi:10.3390/w12010186

Abstract

Experimental turbulence measurements of scour hole downstream of bed sills in alluvial channels with non-cohesive sediments are investigated. Using an Acoustic Doppler Velocimeter (ADV), the flow velocity-field within the equilibrium scour hole was comprehensively measured. In this study, we especially focus on the flow hydrodynamic structure in the scour hole at equilibrium. In addition to the flow velocity distribution in the equilibrium scour hole, the turbulence intensities, the Reynolds shear stresses, the turbulent kinetic energy, and the turbulent length scales are analyzed. Since the prediction of equilibrium scour features is always very uncertain, in this study and based on laboratory turbulence measurements, we apply the phenomenological theory of turbulence to predict the maximum equilibrium scour depth. With this approach, we obtain a new scaling of the maximum scour depth at equilibrium, which is validated using experimental data, satisfying the validity of a spectral exponent equal to −5/3. The proposed scaling shows a quite reasonable accuracy in predicting the equilibrium scour depth in different hydraulic structures.

Highlights

Prediction of maximum scour depth downstream of hydraulic structure i.e., bridge piers and abutments, sills, sluice gates, spillways, weirs, offshore platforms, wind turbines, etc., is of primary concern for a wide range of engineering and environmental applications
By means of velocity measurements, we observed that at equilibrium conditions the flow in the scour hole is fundamentally characterized by three distinct regions: (i) A first region consists of a free entering jet flow, plunging from the crest of bed sill into the scour hole and strongly eroding the bed sediments; (ii) a second region located near the scour bottom, extending upstream as shown in Equations (10) and (11) by the coefficients 1.43 and 0.53
Considering that an exhaustive prediction of the scour development is fundamental for structural stability, we examined experimentally the local scouring processes downstream of hydraulic grade control structures

Summary

Introduction

Prediction of maximum scour depth downstream of hydraulic structure i.e., bridge piers and abutments, sills, sluice gates, spillways, weirs, offshore platforms, wind turbines, etc., is of primary concern for a wide range of engineering and environmental applications. This topic has drawn attention and interest from many researchers for decades [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. Tregnaghi et al [14]

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Conclusion