Effects of Streamwise Ridges on Hydraulic Resistance in Open-Channel Flows

Andrea Zampiron* (Corresponding Author), Vladimir Nikora, Stuart Cameron, Wada Patella, Isacco Valentini, Mark Stewart

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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This Technical Note reports on new experiments focused on hydraulic resistance in open-channel flows over beds covered with streamwise ridges. Extensive bulk friction factor measurements, combined with particle image velocimetry (PIV) for selected cases, were carried out to investigate the effects of spanwise spacing, relative submergence, and surface roughness of the ridges. Two types of ridges were investigated, both characterized by triangular cross sections but featuring different surface roughness. Compared to friction factor estimates neglecting any changes in flow structure promoted by the ridges, the measured friction factors were found to be higher by 10% at ridge spacings of approximately 1.6H and lower by up to 20% at spacings smaller than 0.7H (H is flow depth). No influence of relative submergence and ridge surface roughness on these findings was observed. The PIV data suggest that the revealed effects are likely related to secondary currents instigated and modulated by the bed ridges.

Original languageEnglish
Article number06019018
Number of pages8
JournalJournal of Hydraulic Engineering
Issue number1
Early online date23 Oct 2019
Publication statusPublished - Jan 2020

Bibliographical note

Funding Information:
Financial support was provided by the EPSRC/UK grant “Bed Friction in Rough-Bed Free-Surface Flows: A Theoretical Frame-work, Roughness Regimes, and Quantification” (Grant No. EP/ K041088/1). Discussions with I. Marusic (University of Melbourne) and B. Ganapathisubramani (University of Southampton) are greatly




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