Mean and Turbulent Flow Characteristics in Supercritical Narrow Open Channel Flows: Effect of Froude Number

Demiral, Dila

doi:10.3850/38wc092019-0362

Cited by 2 publications

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“…The tests were conducted under supercritical (Froude number F o > 2), fully turbulent (Reynolds number R o > 2.5 × 10 5 ), and gradually varied open channel flow conditions. It should be noted that in each experiment, the log law applies in the wall layer not only at the centreline but also in traverse locations, revealing that the turbulent flow is fully developed (Demiral, 2019; Demiral et al, 2020). The flow equilibrium parameter β denoting the flow uniformity degree follows (Song & Chiew, 2001):

β goodbreak= \frac{{italicgR}_{h}}{U_{*}^{2}} ((), \frac{{italicdR}_{h}}{dx} goodbreak- S_{b})

Here, R h = A / P = b·h /( b + 2 h ) = hydraulic radius and P = wetted perimeter.…”

Section: Experimental Setup and Instrumentationmentioning

confidence: 96%

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Particle saltation trajectories in supercritical open channel flows: Roughness effect

Demiral

Albayrak

Turowski

et al. 2022

Earth Surf Processes Landf

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Bed load sediment transport governed by particle saltation in supercritical open channel flows causes bedrock incision in high-gradient mountain streams and hydroabrasion at hydraulic structures. Hence, a better understanding of turbulent flow characteristics and particle dynamics is of prime importance for the prediction of river and landscape evolution, and for a sustainable design of hydraulic structures. To this end, we experimentally investigated single-particle dynamics in supercritical open channel flows over fixed planar and abraded beds covering smooth, transitionally rough, and hydraulically rough regimes. The experiments were performed at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of ETH Zürich in a wide range of hydraulic conditions with various channel width-to-depth aspect ratios (b/ h o ) and Froude numbers (F). We investigated the motions of five particle groups differing in shape, hardness, and diameter. By means of a high-speed camera, the particle velocities and trajectory parameters-such as hop height and hop length-were determined using particle tracking velocimetry. The results reveal that at least 120 individual particles should be used in the tests to determine sound statistics of particle trajectories. In the present test conditions, the particles are dominantly transported in saltation. The effects of particle properties such as shape and diameter on the particle trajectories are negligible, while the rolling probability of the particles for a given flow condition increases with increasing diameter. Bed roughness was found to be the key parameter having a significant effect on the saltation trajectories and horizontal energy transfer. Hop height, hop length, and particle velocities, as well as horizontal energy transfer, increase with increasing bed roughness. Based on the saltation trajectory data, non-dimensional equations are developed for each hydraulic regime and used to enhance the saltation-abrasion model of Sklar and Dietrich. The present findings contribute to a better understanding of particle motion characteristics under different hydraulic and roughness conditions, and their effect on the mechanics and prediction of bedrock incision and hydro-abrasion in threedimensional supercritical open channel flows occurring in steeply sloped rivers and at hydraulic structures.

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β goodbreak= \frac{{italicgR}_{h}}{U_{*}^{2}} ((), \frac{{italicdR}_{h}}{dx} goodbreak- S_{b})

Here, R h = A / P = b·h /( b + 2 h ) = hydraulic radius and P = wetted perimeter.…”

Section: Experimental Setup and Instrumentationmentioning

confidence: 96%

“…The results show that all the analysed particles have elliptical shapes with κ R > 1. the centreline but also in traverse locations, revealing that the turbulent flow is fully developed (Demiral, 2019;Demiral et al, 2020). The flow equilibrium parameter β denoting the flow uniformity degree follows (Song & Chiew, 2001):…”

Section: Particle Propertiesmentioning

confidence: 99%