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

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.