Flow Patterns in an Open Channel Confluence with Increasingly Dominant Tributary Inflow

Schindfessel, Laurent; Creëlle, Stéphan; Mulder, Tom De

doi:10.3390/w7094724

Cited by 95 publications

(52 citation statements)

References 31 publications

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“…The experimental tests of Birjukova et al [23] were reproduced by Brito et al [32], comparing the results obtained with different turbulence closure models for solving the RANS equations. More recently, Schindfessel et al [33] used LES of the OpenFOAM suite to investigate the flow patterns for three different Q r , considering the experimental tests by Schindfessel et al [22]. They demonstrated that the tributary flow impinges on the opposing bank when the tributary flow becomes sufficiently dominant, causing a recirculating eddy in the upstream channel of the confluence, which induces significant changes in the incoming velocity distribution.…”

Section: Introductionmentioning

confidence: 99%

Effect of the Junction Angle on Turbulent Flow at a Hydraulic Confluence

Penna

Marchis

Canelas

et al. 2018

Water

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Despite the existing knowledge concerning the hydrodynamic processes at river junctions, there is still a lack of information regarding the particular case of low width and discharge ratios, which are the typical conditions of mountain river confluences. Aiming at filling this gap, laboratory and numerical experiments were conducted, comparing the results with literature findings. Ten different confluences from 45 • to 90 • were simulated to study the effects of the junction angle on the flow structure, using a numerical code that solves the 3D Reynolds Averaged Navier-Stokes (RANS) equations with the k-turbulence closure model. The results showed that the higher the junction angle, the wider and longer the retardation zone at the upstream junction corner and the separation zone, and the greater the flow deflection at the entrance of the tributary into the post-confluence channel. Furthermore, it was shown that the maximum streamwise velocity does not necessarily increase with the junction angle and that it is not always located in the contraction section.

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Section: Introductionmentioning

confidence: 99%

Effect of the Junction Angle on Turbulent Flow at a Hydraulic Confluence

Penna

Marchis

Canelas

et al. 2018

Water

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“…Yuan et al (2016) also observed a clear hump in the transverse velocity spectra, very similar to our observations in the centre of the channel (Figures 11B and 11C). Unfortunately, comparison with other confluences is limited as very few studies at confluences have provided a detailed turbulent analysis of the lateral velocity component in the mixing zone, with the studies of Schindfessel et al (2015) and Yuan et al (2016) in 90°laboratory junctions and modelling studies being the exception.…”

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confidence: 99%

Three‐dimensional turbulent structures at a medium‐sized confluence with and without an ice cover

Biron

Buffin‐Bélanger

Martel

2019

Earth Surf Processes Landf

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River confluences are characterized by a complex mixing zone with three‐dimensional (3D) turbulent structures which have been described as both streamwise‐oriented structures and Kelvin–Helmholtz (KH) vertical‐oriented structures. The latter are visible where there is a turbidity difference between the two tributaries, whereas the former are usually derived from mean velocity measurements or numerical simulations. Few field studies recorded turbulent velocity fluctuations at high frequency to investigate these structures, particularly at medium‐sized confluences where logistical constraints make it difficult to use devices such as acoustic doppler velocimeter (ADV). This study uses the ice cover present at the confluence of the Mitis and Neigette Rivers in Quebec (Canada) to obtain long‐duration, fixed measurements along the mixing zone. The confluence is also characterized by a marked turbidity difference which allows to investigate the mixing zone dynamics from drone imagery during ice‐free conditions. The aim of the study is to characterize and compare the flow structure in the mixing zone at a medium‐sized (~40 m) river confluence with and without an ice cover. Detailed 3D turbulent velocity measurements were taken under the ice along the mixing plane with an ADV through eight holes at around 20 positions on the vertical. For ice‐free conditions, drone imagery results indicate that large (KH) coherent structures are present, occupying up to 50% of the width of the parent channel. During winter, the ice cover affects velocity profiles by moving the highest velocities towards the centre of the profiles. Large turbulent structures are visible in both the streamwise and lateral velocity components. The strong correlation between these velocity components indicates that KH vortices are the dominating coherent structures in the mixing zone. A spatio‐temporal conceptual model is presented to illustrate the main differences on the 3D flow structure at the river confluence with and without the ice cover. © 2019 John Wiley & Sons, Ltd.

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“…The mixing of the two inflows is analysed by setting the dimensionless concentration of passive scalar at 1 in one inflow and at 0 in the other. As the Froude number is lower than 0.3, we use a rigid lid assumption [7] for the free surface.…”

Section: Numerical Modelmentioning

confidence: 99%

“…In the last decade, 3D numerical methods have shown their ability to fairly compute the hydrodynamics of the flow in open-channel confluences [5], [6], [7], [1]. However detailed databases of passive scalar concentration within such confluences and downstream branches is lacking in the literature and thus does not permit to validate the 3D numerical codes, either advanced (LES or DES) or more operational codes (RANS) regarding their capacity to fairly reproduce the mixing processes.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulations on mixing of passive scalars in river confluences

et al. 2018

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The study deals with the mixing of passive scalars (such as pollutants) in open-channel confluences when the two inflows exhibit different concentrations. The dispersion of such passive scalars is investigated through the analysis of the processes enhancing the mixing in the confluence in order to estimate the length for complete mixing Lm in the downstream branch. The aim of this study is then to establish a correlation between this length for complete mixing Lm and characteristics of the confluence, namely its angle and two hydrodynamic parameters that are the momentum ratio M* of the inflows and the width-to-depth ratio of the downstream branch b/h. In this work, the flow in the confluence is numerically simulated by RANS calculation coupled with the advection-diffusion equation at field scale, i.e. with Reynolds and Froude numbers corresponding to real rivers (Re = 107 and Fr=0.1). The role of other parameters such as bed discordance or bed forms... is not addressed here. The numerical results highlight that the mixing in the confluence and its downstream branch, is enhanced by the presence of secondary currents that are themselves strongly affected by the characteristics of the confluence. The results aim at getting an operative empirical law linking the geometric and hydrodynamic parameters of the confluence with Lm.

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Flow Patterns in an Open Channel Confluence with Increasingly Dominant Tributary Inflow

Cited by 95 publications

References 31 publications

Effect of the Junction Angle on Turbulent Flow at a Hydraulic Confluence

Effect of the Junction Angle on Turbulent Flow at a Hydraulic Confluence

Three‐dimensional turbulent structures at a medium‐sized confluence with and without an ice cover

Numerical simulations on mixing of passive scalars in river confluences

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