Flow development in rough-bed open channels: mean velocities, turbulence statistics, velocity spectra, and secondary currents. Issue 1 (2nd January 2023)

• Record Type: Journal Article
• Authors: Zampiron, Andrea; Cameron, Stuart M.; Stewart, Mark T.; Marusic, Ivan; Nikora, Vladimir I.
• Is Part Of: Journal of hydraulic research. Volume 61:Issue 1(2023)
• Page Start: 133
• Page End: 144
• Publication Date: 2023-01-02
• Subjects: Coherent structures -- hydraulic experiments -- open-channel flow -- velocity spectra -- turbulence; Hydraulics -- Research -- Periodicals; Hydraulic engineering -- Periodicals; Hydraulic engineering; Electronic journals; Periodicals; 621.2
• DOI: 10.1080/00221686.2022.2132311
• Languages: English
• ISSNs: 0022-1686

Abstract

Abstract : The channel length required for the development of the flow, from the channel entrance to full establishment, is often a prerequisite when designing hydraulic structures or planning research experiments in open channels. However, the information on the flow development length ( L D ) is scarce, and even its definition remains vague. In hydraulic experiments, this lack of knowledge introduces great uncertainty, often making comparisons of findings from different studies questionable. This paper offers a physics-based definition for L D, and reports results of systematic laboratory studies to provide guidance on its quantitative assessment. Our data for uniform flows suggest that up to 100 flow depths ( H ) are required for mean velocity field (including sidewall secondary currents), turbulent stresses (except streamwise variance), velocity skewness and kurtosis, and depth-scale large-scale-motions to become essentially independent of the streamwise coordinate. However, very large-scale-motions, streamwise velocity variance, and roughness-induced secondary currents are found to require longer L D of around 150 H .