Turbulent non-uniform flows in straight compound open-channels

Proust, Sébastien; Fernandes, J. N.; Peltier, Yann; Leal, J. B.; Rivière, Nicolas; Cardoso, António H.

doi:10.1080/00221686.2013.818586

Cited by 45 publications

(35 citation statements)

References 24 publications

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“…We use depth‐averaged values as commonly done for uniform flows [ Shiono and Knight , ]. The depth‐averaged and time‐averaged transverse exchange of streamwise momentum has three contributions [ Proust et al ., ]:

\overset{\frac{1}{h} true \int_{0}^{h} - ρ u v d z}{true} = - ρ {\overset{true¯}{true(u^{'} v^{'} true)}}_{d} - ρ U_{d} V_{d} - ρ {[U (V - V_{d})]}_{d}

where h is local flow depth and

ρ

is fluid density. The first contribution is the depth‐averaged Reynolds‐stress, the term

- ρ U_{d} V_{d}

is the momentum transfer by the transverse flow, and the term

- ρ {[U (V - V_{d})]}_{d}

is the depth‐averaged momentum transfer by the secondary currents.…”

Section: Effect Of the Three Forcingsmentioning

confidence: 99%

“…Starting with uniform flow conditions, nonuniform flows are generated by imposing an imbalance in the upstream discharge distribution between subsections, keeping the total discharge constant. From a practical point of view, the study of unbalanced inflow conditions is interesting, because the velocity distribution is necessarily out of equilibrium at the upstream boundary of a compound reach [ Proust et al ., ]. For instance, an excess in FP inflow can be caused by narrowing FPs upstream of the studied reach [ Bousmar et al ., ], or by an abrupt FP contraction [ Proust et al ., ] in which a 34% flow excess was measured.…”

Section: Introductionmentioning

confidence: 99%

“…The effect of a transverse flow on Reynolds‐stresses was studied by Proust et al . [] for a single D r ‐value ( D r ∼ 0.3). It was shown that, for a fixed downstream position, and with an increasing transverse flow to the MC, the region of high values of Reynolds‐stress was laterally and vertically stretched by the plunging flow into the MC.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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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\overset{\frac{1}{h} true \int_{0}^{h} - ρ u v d z}{true} = - ρ {\overset{true¯}{true(u^{'} v^{'} true)}}_{d} - ρ U_{d} V_{d} - ρ {[U (V - V_{d})]}_{d}

where h is local flow depth and

ρ

is fluid density. The first contribution is the depth‐averaged Reynolds‐stress, the term

- ρ U_{d} V_{d}

is the momentum transfer by the transverse flow, and the term

- ρ {[U (V - V_{d})]}_{d}

is the depth‐averaged momentum transfer by the secondary currents.…”

Section: Effect Of the Three Forcingsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

View full text Add to dashboard Cite

show abstract

“…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%

“…These studies showed that the lateral momentum exchange between the main channel flow and the floodplain flow is driven by both the turbulent diffusion related to the mixing layer that forms at the main channel/floodplain interface and by the net lateral mass transfers between main channel and floodplain. Proust et al (2013) investigated the relaxation of flows in a straight smooth compound channel in which the upstream discharge distribution between main channel and floodplain was destabilized with regards to the uniform discharge distribution. It appears that the relaxation to uniformity is a relatively slow process: for an excess or a deficit in floodplain discharge of ± 19% at the flume inlet, the uniform discharge distribution is not reached 10 m downstream.…”

Section: Introductionmentioning

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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MATLAB‐based program for computation of open‐channel flow profiles

Shen

et al. 2023

Comp Applic In Engineering

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In engineering practice, open channel water surface profile data frequently serve as the scientific foundation for engineering design, flood forecasting, reservoir scheduling, and the calculation of dam-break flood evolution. Water surface profiles in open channels (WSPOC), Matrix Laboratory (MATLAB)based software was developed to help students better learn and improve their interest in surface line theory. According to the flow characteristics, the program is divided into two modules: steady flow and unsteady flow. The steady flow module guides students to master the judgment methods of various gradually varying flow types and can program independently to explore the solution process of the water surface profiles. The unsteady flow module is designed to help students learn finite difference methods in computational fluid dynamics (CFD), and allow students to interact with software in engineering cases to achieve the purpose of effectively integrating theory and practice. This software employs MATLAB graphical user interface (GUI) visualization technology to embed students' autonomous programming in crucial phases and transforms abstract concepts and theories into vivid animation demonstrations using CFD simulation tools. Furthermore, the transformation from theory to practice has been realized by providing a large number of practical engineering examples, which may improve students' ability to solve complex engineering problems. Based on the survey results, the user experience and application effect of the software are satisfactory, and the software's design objective has been achieved.

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Turbulent non-uniform flows in straight compound open-channels

Cited by 45 publications

References 24 publications

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

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

MATLAB‐based program for computation of open‐channel flow profiles

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