Turbulent flows in straight compound open-channel with a transverse embankment on the floodplain

Peltier, Yann; Proust, Sébastien; Rivière, Nicolas; Paquier, André; Shiono, K.

doi:10.1080/00221686.2013.796499

Cited by 22 publications

(19 citation statements)

References 24 publications

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“…These changes in the lateral position, y 0.1 and the mixing layer width were also observed by Peltier et al (2013a) in the LMFA flume with a transverse embankment set on the floodplain. With the same total flow rate Q = 24.7 l/s, and with a 50 cm-long embankment, the width δ is zero close to the embankment owing to very large transverse flows.…”

Section: Depth-averaged Transverse Flowmentioning

confidence: 72%

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Turbulent non-uniform flows in straight compound open-channels

Proust¹,

Fernandes

Peltier³

et al. 2013

Journal of Hydraulic Research

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The reported experimental study assesses the effects of flow non-uniformity on the momentum flux in straight compound channels. Two flumes were used, featuring vertical and sloping banks. Starting with uniform flow condition, various imbalances in the upstream discharge distribution were introduced. This resulted in a time-averaged lateral flow and advective transport of momentum, which interacted with the shear-layer turbulence generated by the compound geometry. To investigate this interaction, the three contributions to transverse momentum flux (depth-averaged flow, shear-layer turbulence and dispersive term of spanwise velocity) are assessed. The first two contributions were strengthened by the sloping banks, while the third becomes important for the case of the vertical bank. With a lateral flow towards the main channel, the first contribution rises at the expense of the second. With a lateral flow towards the floodplain, the first two contributions have the same order of magnitude, and the Boussinesq approach is invalidated.

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Section: Depth-averaged Transverse Flowmentioning

confidence: 72%

“…Additional values of δ are displayed for the uniform flow at LMFA (nine measuring sections). They were obtained from U d -profiles that were measured byPeltier et al (2013a) with identical flow conditions in the same flume. With the uniform flows inFig.…”

mentioning

confidence: 99%

Turbulent non-uniform flows in straight compound open-channels

Proust¹,

Fernandes

Peltier³

et al. 2013

Journal of Hydraulic Research

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“…Lastly, to get a better insight into the transverse development of the mixing layer, mean flow data collected by Peltier et al . [] in the LMFA flume under uniform flow conditions were also used.…”

Section: Experimental Apparatus and Measuring Techniquesmentioning

confidence: 99%

“…The effect of a transverse flow on shear layer turbulence was evaluated by Peltier et al . [] for rapidly varied flows caused by a transverse embankment located on the FP. In all these nonprismatic geometries, mass and momentum exchanges are strongly linked to the type of geometry studied.…”

Section: Introductionmentioning

confidence: 99%

Mixing layer and coherent structures in compound channel flows: Effects of transverse flow, velocity ratio, and vertical confinement

Proust

Fernandes

Leal

et al. 2017

Water Resources Research

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Turbulent mixing layers associated with streamwise uniform and nonuniform flows in compound channels (main channel with adjacent floodplains) are experimentally investigated. The experiments start with uniform flow conditions. The streamwise nonuniformity is then generated by imposing an imbalance in the upstream discharge distribution between main channel (MC) and floodplains (FPs), keeping the total discharge constant, which results in a transverse depth‐averaged mean flow. This study first aims at assessing the effect of a transverse flow on the mixing layer and coherent structures that form at the MC/FP interfaces. A wide range of initial velocity ratio or dimensionless shear between MC and FP is tested. The study second aims at assessing the effect of this velocity ratio on the mixing layer, for a fixed vertical confinement of flow. The total discharge was then varied to quantify the confinement effect. The results show that, far from the inlet section, Reynolds‐stresses increase with local velocity ratio for a fixed confinement and decrease with confinement for a fixed velocity ratio. It is also shown that, irrespective of confinement, the existence of quasi‐two‐dimensional coherent structures is driven by velocity ratio and the direction and magnitude of transverse flow. These structures cannot develop if velocity ratio is lower than 0.3 and if a strong transverse flow toward the MC occurs. In the latter case, the transverse flow is the predominant contribution to momentum exchange (compared with turbulent mixing and secondary currents), convex mean velocity profiles are observed, preventing the formation of quasi‐two‐dimensional structures.

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“…The position of y IP is (2013), we do not detect a lateral displacement of y IP when mass is transferred from the floodplain to the main channel. This may be due to weaker mass transfers than in the experiments of Proust et al (2013) and Peltier et al (2013). Figure 8a shows the position y U0 relative to the position y int for all test cases.…”

Section: Mixing Layer Centrementioning

confidence: 99%

Compound channel flow with a longitudinal transition in hydraulic roughness over the floodplains

et al. 2017

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Transitions from submerged dense vegetation (meadow) to emergent rigid vegetation (wood) and vice versa are modelled using plastic grass and vertical wooden cylinders. For a given roughness transition, the upstream discharge distribution between main channel and floodplain (called subsections) is also varied, keeping the total flow rate constant. The flows with a roughness transition are compared to flows with a uniformly distributed roughness over the whole length of the flume. Besides the influence of the downstream boundary condition, the longitudinal profiles of water depth are controlled by the upstream discharge distribution. The latter also strongly influences the magnitude of the lateral net mass exchanges between subsections, especially upstream from the roughness transition. Irrespective of flow conditions, the inflection point in the mean velocity profile across the mixing layer is always observed at the interface between subsections. The longitudinal velocity at the main channel/floodplain interface, denoted U int , appeared to be a key parameter for characterising the flows. First, the mean velocity profiles across the mixing layer, normalised using U int , are superimposed irrespective of downstream position, flow depth, floodplain roughness type and lateral mass transfers. However, the profiles of turbulence quantities do not coincide, indicating that the flows are not fully self-similar and that the eddy viscosity assumption is not valid in this case. Second, the depth-averaged turbulent intensities and Reynolds stresses, when scaled by the depth-averaged velocity U d,int exhibit two plateau values, each related to a roughness type, meadow or wood. Lastly, the same results hold when scaling by U d,int the depth-averaged lateral flux of momentum due to secondary currents. Turbulence production and magnitude of secondary currents are increased by the presence of emergent rigid elements over the floodplains. The autocorrelation functions show that the length of the coherent structures scales with the mixing layer width for all flow cases. It is suggested that coherent structures tend to a state where the magnitude of velocity fluctuations (of both horizontal vortices and secondary currents) and the spatial extension of the structures are in equilibrium.

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Turbulent flows in straight compound open-channel with a transverse embankment on the floodplain

Cited by 22 publications

References 24 publications

Turbulent non-uniform flows in straight compound open-channels

Turbulent non-uniform flows in straight compound open-channels

Mixing layer and coherent structures in compound channel flows: Effects of transverse flow, velocity ratio, and vertical confinement

Compound channel flow with a longitudinal transition in hydraulic roughness over the floodplains

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