Three-Dimensional Numerical Investigations of the Flow Pattern and Evolution of the Horseshoe Vortex at a Circular Pier during the Development of a Scour Hole

Ahmed M Helmi,Ahmed H Shehata

doi:10.3390/app11156898

Abstract

In the current study, a three-dimensional CFD model is utilized to investigate the variation of the flow structure and bed shear stress at a single cylindrical pier during scour development. The scour development is presented by seven solidified geometries of the scour hole, collected during previous experimental work at different scour stages. Different turbulence models are evaluated and the (k-ω) model is chosen due to its relative accuracy in capturing the flow oscillation and vortex shedding at the pier downstream side with personal computer computational and storage resources. The numerical results are verified against dimensionless parameters from different previous experimental works. This research describes in detail the flow structure and bed shear stress variations through seven stages of the scour hole development. The dimensionless area-averaged circulation coefficient (Ψi) is developed to evaluate the changes in the vortex strength through the scouring process by eliminating the calculation area effect. It was concluded that the circulation in the (Y) direction is the main driving factor in the development of the scour hole more than the circulation in the (X) direction. The ratio between the horseshoe vortex (HV) mean size and the scouring depth (DV/dS) in addition to the location of the maximum bed shear stress are investigated during different stages of the scour development.

Highlights

The majority of bridge failure incidents are caused by the scour phenomenon at bridge pier foundations
A better understanding of the flow structure and the bed shear stress distribution around bridge piers will enhance the prediction of the scour depth, and will reduce the bridge construction cost
These observations indicate that as the scour hole developed, the horseshoe vortex (HV) sunk inside the hole and moved further below the original bed level, which is in agreement with the experimental observations by the author of [14]

Summary

Introduction

The majority of bridge failure incidents are caused by the scour phenomenon at bridge pier foundations. The level and the type of bridge pier foundations are directly related to the scour depth that has a significant impact on the bridge’s construction cost. A better understanding of the flow structure and the bed shear stress distribution around bridge piers will enhance the prediction of the scour depth, and will reduce the bridge construction cost. Numerous laboratory studies have been carried out to develop equations to predict the maximum scour depth [1,2,3,4,5,6,7,8,9]. In subcritical flow conditions where the Froude number < 1, the maximum ratio between the equilibrium scour depth and the pier diameter (dse /D) was experimentally obtained around 2.4 [11].

Methods

Results

Conclusion