Prediction of flow around a sharp-nosed bridge pier: influence of the Froude number and free-surface variation on the flow field

Recep Kahraman,Matthew Riella,Gavin R Tabor,Mohsen Ebrahimi,Slobodan Djordjević,Prakash Kripakaran

doi:10.1080/00221686.2019.1631223

Abstract

This study investigates the influence of free-surface variation on the velocity field using numerical simulations of flow around a sharp-nosed pier that is representative of a typical masonry bridge pier. The study evaluates the assumption that free-surface effects are negligible at small Froude numbers by comparing the change in flow field predictions due to the use of a free-surface model (i.e. multi-phase simulation with a volume of fluid (VOF) model in place of a rigid-lid approximation (i.e. single phase simulation). Results show that simulations using the VOF model are in better agreement with experimental data than those using the rigid-lid approximation. Importantly, results show that even though the change in free-surface height near the pier is small comparative to the approach flow, it still has a significant effect on velocities in front of the pier and in the wake region, and including at low Froude numbers.

Highlights

The flow around hydraulic structures such as bridge piers is very complex due to the constant shearing of the approaching flow generating multiple vortex systems and complicated free-surface interactions
Understanding the flow around masonry bridge piers and their impact on scour is of critical importance in the context of flood resilience of transport networks
To facilitate the validation and comparison of the experimental and numerical models, the measured and predicted streamwise components of velocities are compared in both depthwise and spanwise directions

Summary

Introduction

The flow around hydraulic structures such as bridge piers is very complex due to the constant shearing of the approaching flow generating multiple vortex systems (e.g. horseshoe, lee-wake systems) and complicated free-surface interactions These processes are largely responsible for the initiation and development of scour (Breusers, Nicollet, & Shen, 1977), a phenomenon that can have a significant deleterious effect on the structural integrity of bridges, during flood events. Masonry bridge piers are at high risk of scour due to their large width-to-length ratio and their unique geometries, which often includes triangle cut-waters (i.e. sharp noses) These structures make up nearly 40% of the UK’s current bridge stock with a significant number listed as cultural and engineering heritage structures. Understanding the flow around masonry bridge piers and their impact on scour is of critical importance in the context of flood resilience of transport networks

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