Compound open-channel flows: effects of transverse currents on the flow structure

Proust, Sébastien; Nikora, Vladimir

doi:10.1017/jfm.2019.973

Cited by 47 publications

(93 citation statements)

References 52 publications

(130 reference statements)

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“…Third, the helical secondary currents (SCs) with a longitudinal axis that are observed in uniform flows (Knight & Shiono, 1990; Tominaga & Nezu, 1991) and which are induced by the compound channel topography and flow heterogeneity can be altered by transverse currents between MC and FP (called herein the subsections). This was observed in compound meandering channels (Shiono & Muto, 1998), in the presence of converging FPs (Bousmar et al, 2004; Proust et al, 2006), and also for nonuniform flows in a straight compound channel (Proust & Nikora, 2020). Lastly, the latter authors have observed that transverse currents had less impact on the horizontal Kelvin‐Helmholtz‐type coherent structures (KHCSs) that may populate the planform shear layer than on the shear layer itself.…”

Section: Introductionmentioning

confidence: 88%

“…x u ′ (Proust & Nikora, 2020). For the one-point velocity measurements, transverse velocity profiles at a fixed elevation z * (i.e., 21 mm from the FP bed for case 8 L s −1 , and 17 mm for the other cases) and various x * -positions were measured, and full half cross-sections at three x * -positions were also covered (measurements at intervals of 4 to 10 mm in the vertical direction at 17 z * -elevations in the MC including 5 above the bank full stage, and at 3 to 5 z * -elevations over the FP depending on flow conditions; and measurements at intervals of 10 to 100 mm in the lateral direction at 40 y * -positions in a half cross-section).…”

Section: Measuring Techniquesmentioning

confidence: 99%

“…For instance, for case Qf20 (Figure 8, plots c1, c2, and c3), a strong reduction in the velocity u x can be observed in the upper part of the flow (for z * ≥ 0.07) due to the entrance of slow momentum fluid coming from the FP in the MC flow. This is explained in Proust and Nikora (2020) by the predominance of the transverse currents in the lateral exchange of streamwise momentum in the first half of the flume (compared to the contributions of KHCSs and SCs to this exchange).…”

Section: Velocities In the Main Channelmentioning

confidence: 99%

“…In the experiments of Proust and Nikora (2020), the emergence and development of KHCSs were investigated based on two-point velocity measurements (see section 2.3) and associated space correlation functions of the velocity fluctuations. Focusing on the spanwise velocity fluctuations, the two following space correlation functions were used in the streamwise and spanwise directions, respectively:…”

Section: Space Correlation Functionsmentioning

confidence: 99%

“…First, they can laterally displace the planform shear layer (based on the transverse distribution of streamwise time‐averaged velocity) over FPs or in MC depending on their direction and magnitude. This was observed in laboratory flumes, for example, in a skewed two‐stage flood channel (Elliot & Sellin, 1990), in a straight compound channel with a transverse embankment set over the FP (Peltier et al, 2013), in a compound open‐channel with narrowing FPs (Bousmar et al, 2004) and diverging FPs (Bousmar et al, 2006; Proust, 2005), and for nonuniform flows in straight compound channels (Proust & Nikora, 2020; Proust et al, 2013). Second, the transverse currents can also displace the turbulence statistics over FPs or in MC, as observed by Peltier et al (2013) and Proust et al (2013).…”

Section: Introductionmentioning

confidence: 99%

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Nonuniform Flows in a Compound Open‐Channel: Assessment of a Hybrid RANS‐LES Approach

Chatelain

Proust

2020

Water Resources Research

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Overbank flows in rivers, also termed compound open-channel flows, are rarely uniform in the streamwise direction. Flow nonuniformity involves transverse currents directed from the river main channel (MC) to adjacent floodplains (FPs) or vice versa. Depending on their direction and magnitude, the transverse currents can laterally displace the planform shear layer that forms at the interface between MC and FP. They can also modify the cross-sectional distribution of the helical secondary currents (SCs). This paper reports a numerical study that focuses on assessing the ability of a hybrid RANS (Reynolds Averaged Navier-Stokes)-LES (Large Eddy Simulation) approach, namely, the Scale Adaptive Simulation (SAS), to capture the evolving structure of both depth-uniform and nonuniform flows in a straight compound open-channel. The simulated flows have recently been studied in an 18 m long and 3 m wide laboratory flume by Proust and Nikora (2020, https://doi.org/10.1017/jfm.2019.973). The originality of the study lies in the modeling of flows over the entire flume length and in the estimate of the length-scales of the large Kelvin-Helmholtz-type coherent structures (KHCSs). The SAS approach can accurately predict the longitudinal evolution of: (i) the streamwise time-averaged flow, including the planform shear layer width, (ii) the SC patterns, and (iii) the turbulence statistics. The emergence and development of the KHCSs are qualitatively retrieved and are confirmed to be controlled by dimensionless velocity shear irrespective of flow depth. The simulations also show that SC patterns depend on the magnitude and direction of the transverse currents and also on the development of KHCSs.

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Section: Introductionmentioning

confidence: 88%

Section: Measuring Techniquesmentioning

confidence: 99%

Section: Velocities In the Main Channelmentioning

confidence: 99%

Section: Space Correlation Functionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nonuniform Flows in a Compound Open‐Channel: Assessment of a Hybrid RANS‐LES Approach

Chatelain

Proust

2020

Water Resources Research

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Flow behaviour in a multi‐layered vegetated floodplain region of a compound channel

Barman

Kumar

2022

Ecohydrology

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Riparian vegetation plays a crucial role in determining the flow behaviour in the channel. The effect of flow on the slope and main channel varies based on the size, type, and density of floodplain vegetation in a compound channel. Though real field vegetation distribution is non‐uniform, most studies mainly concentrate on uniformly distributed vegetation with fixed vegetation height. This paper attempts to address this issue through laboratory studies as it was not explored properly. Flow properties like velocity, Reynolds shear stress, turbulence intensities, and turbulent kinetic energy behave differently in heterogeneous vegetated channel compared with the homogeneous vegetated channel. These flow properties in the slopes and main channel section are more pronounced for uniformly distributed vegetation than non‐uniform distribution. The multi‐layered/varying vegetation height showed higher velocity, turbulent intensity, and turbulent kinetic energy than single‐layered/constant vegetation height on slopes and main channel sections. Integral scales (Taylor and Euler) analysis showed greater magnitude for uniform multi‐layered vegetation than non‐uniform multi‐layered vegetation. Further, the study of octant analysis reveals that internal outward and internal inward interaction events dominate the slope floodplain interaction section, which is not seen in no‐vegetation cases. These studies give a better perspective to understand flow in heterogenous vegetation and move closer to real field scenarios.

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Importance of vegetation in riverbank resilience: An experimental approach

Barman,

Kumar

2024

Earth Surf Processes Landf

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Floodplain (FP) vegetation determines the flow structures in river channels based on its shape, type, spacing and root‐soil binding capacity. The present study focuses on experimental approach to understand the role of FP vegetation in determining the flow patterns and morphological changes in the channels. Flow properties like streamwise and transverse velocity, along with secondary flow and turbulent kinetic energy, were compared between rectangular and compound channels considering partial vegetation cover. The presence and absence of dip phenomenon in the main channel (MC) of compound and rectangular channel respectively suggest that the dip phenomenon is influenced by both vegetation emergence in FPs and differential cross‐sectional depths of compound channels. The secondary flow direction in the slopes and MC of compound channel is towards the FP region which is opposite to that observed in rectangular channel where secondary flow is towards MC showing the effect of non‐uniform cross‐section of compound channels. The morphological changes were analysed by performing experiments in unsymmetrical erodible riverbank channels with bankfull condition considering artificial rigid FP vegetation (Phragmites karka) and naturally growing flexible vegetation (Oryza sativa). After more than 24 h of continuous experimental runs, the O. sativa remains intact in the soil because of development of strong root‐soil bond whereas; all the P. karka gets uprooted. The channel cross‐section in the downstream channel becomes almost uniform for P. karka, whereas differential cross‐sectional height is observed for O. sativa. This study shows that along with the shapes and size of vegetation, root‐soil binding capacity also determines the morphological changes in river channels. Furthermore, it also shows the importance of growing vegetation in the laboratory to properly simulate vegetation observed in river channels.

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Compound open-channel flows: effects of transverse currents on the flow structure

Cited by 47 publications

References 52 publications

Nonuniform Flows in a Compound Open‐Channel: Assessment of a Hybrid RANS‐LES Approach

Nonuniform Flows in a Compound Open‐Channel: Assessment of a Hybrid RANS‐LES Approach

Flow behaviour in a multi‐layered vegetated floodplain region of a compound channel

Importance of vegetation in riverbank resilience: An experimental approach

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