Experimental study of granular bed erosion and sedimentation subjugated to the secondary flow structures in curved ducts

Claudio Faria Duarte,Nima Nadim,Tilak T Chandratilleke

doi:10.1177/1687814019885255

Abstract

This article presents an experimental study on the dynamic behaviour of granular material that forms the bed of a curved fluid flow passage. The secondary vortex structures induced by the passage curvature profoundly influence the stability of the granular material and determine the varying bed profiles subjected to the processes of erosion and sedimentation in the flow passage. For examining the characteristics of the bed profile, the current study develops a non-intrusive measurement method whereby transient changes occurring at the granular bed interface are captured for a range of flow operating conditions. The test results indicate three distinct regimes of onset, transition and quasi-stable erosion–sedimentation in the curved passage over the experimental test range. Each stage is analysed and discussed for the observed intricacies of the flow structures and the bed reshaping behaviour, with respect to the timescale of these occurrences, influences of the flow rate and granular particle size.

Highlights

The presence of the secondary vortex structures, inclusive of Dean vortices, is a well-known flow feature in curved flow passages, giving rise to additional fluid mixing, flow turbulence and pressure drop
In a curved passage with a bed of granular material, when the fluid flow is sufficiently strong, wall shear imparted by the secondary flow structure tends to dislodge granular particles and shift them radially over the School of Civil and Mechanical Engineering, Curtin University, Perth, WA, Australia
The current study addresses this shortfall through an experimental investigation of erosion and sedimentation processes in a curved passage with granular material forming the bed of the flow passage

Summary

Introduction

The presence of the secondary vortex structures, inclusive of Dean vortices, is a well-known flow feature in curved flow passages, giving rise to additional fluid mixing, flow turbulence and pressure drop. In a curved flow passage, the mechanistic principle of centrifugal action induces radially driven fluid motion to produce the secondary flow. This radial motion combines with the axial fluid flow and establishes a unique vortex flow structure in curved passages, making these flow patterns vastly different to those in straight ducts. In a curved passage with a bed of granular material, when the fluid flow is sufficiently strong, wall shear imparted by the secondary flow structure tends to dislodge granular particles and shift them radially over the School of Civil and Mechanical Engineering, Curtin University, Perth, WA, Australia

Methods

Results

Conclusion