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Open AccessArticle

A Numerical Study of the Influence of Channel-Scale Secondary Circulation on Mixing Processes Downstream of River Junctions

1
Institute of Continuous Media Mechanics, Ural Branch of the Russian Academy of Science, 614013 Perm, Russia
2
Department of Theoretical Physics, Perm State University, 614990 Perm, Russia
3
Mining Institute UB RAS, 614007 Perm, Russia
4
Department of Civil, Architectural and Environmental Engineering, University of Napoli “Federico II”, 80138 Napoli, Italy
5
Ecole Centrale, CNRS, Aix-Marseille Université, 13007 Marseille, France
6
Institute of Earth Surface Dynamics, Université de Lausanne, 1015 Lausanne, Switzerland
*
Author to whom correspondence should be addressed.
Water 2020, 12(11), 2969; https://doi.org/10.3390/w12112969
Received: 26 August 2020 / Revised: 19 October 2020 / Accepted: 20 October 2020 / Published: 23 October 2020
(This article belongs to the Section Hydrology and Hydrogeology)
A rapid downstream weakening of the processes that drive the intensity of transverse mixing at the confluence of large rivers has been identified in the literature and attributed to the progressive reduction in channel scale secondary circulation and shear-driven mixing with distance downstream from the junction. These processes are investigated in this paper using a three-dimensional computation of the Reynolds averaged Navier Stokes equations combined with a Reynolds stress turbulence model for the confluence of the Kama and Vishera rivers in the Russian Urals. Simulations were carried out for three different configurations: an idealized planform with a rectangular cross-section (R), the natural planform with a rectangular cross-section (P), and the natural planform with the measured bathymetry (N), each one for three different discharge ratios. Results show that in the idealized configuration (R), the initial vortices that form due to channel-scale pressure gradients decline rapidly with distance downstream. Mixing is slow and incomplete at more than 10 multiples of channel width downstream from the junction corner. However, when the natural planform and bathymetry are introduced (N), rates of mixing increase dramatically at the junction corner and are maintained with distance downstream. Comparison with the P case suggests that it is the bathymetry that drives the most rapid mixing and notably when the discharge ratio is such that a single channel-scale vortex develops aided by curvature in the post junction channel. This effect is strongest when the discharge of the tributary that has the same direction of curvature as the post junction channel is greatest. A comprehensive set of field data are required to test this conclusion. If it holds, theoretical models of mixing processes in rivers will need to take into account the effects of bathymetry upon the interaction between river discharge ratio, secondary circulation development, and mixing rates. View Full-Text
Keywords: confluence of two rivers; secondary flows; three-dimensional numerical modeling; weakening of transverse mixing confluence of two rivers; secondary flows; three-dimensional numerical modeling; weakening of transverse mixing
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MDPI and ACS Style

Lyubimova, T.P.; Lepikhin, A.P.; Parshakova, Y.N.; Kolchanov, V.Y.; Gualtieri, C.; Roux, B.; Lane, S.N. A Numerical Study of the Influence of Channel-Scale Secondary Circulation on Mixing Processes Downstream of River Junctions. Water 2020, 12, 2969. https://doi.org/10.3390/w12112969

AMA Style

Lyubimova TP, Lepikhin AP, Parshakova YN, Kolchanov VY, Gualtieri C, Roux B, Lane SN. A Numerical Study of the Influence of Channel-Scale Secondary Circulation on Mixing Processes Downstream of River Junctions. Water. 2020; 12(11):2969. https://doi.org/10.3390/w12112969

Chicago/Turabian Style

Lyubimova, Tatyana P.; Lepikhin, Anatoly P.; Parshakova, Yanina N.; Kolchanov, Vadim Y.; Gualtieri, Carlo; Roux, Bernard; Lane, Stuart N. 2020. "A Numerical Study of the Influence of Channel-Scale Secondary Circulation on Mixing Processes Downstream of River Junctions" Water 12, no. 11: 2969. https://doi.org/10.3390/w12112969

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