Flow hydrodynamics, density contrast effects and mixing at the confluence between the Yangtze River and the Poyang Lake channel

Jiang, Chenyu; Constantinescu, George; Yuan, Saiyu; Tang, Hongwu

doi:10.1007/s10652-022-09848-3

Cited by 17 publications

(18 citation statements)

References 65 publications

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“…In this regard, the present results obtained for a canonical geometry (constant-depth channel, zero confluence angle, no SOV cells generated by the change in the direction of the incoming streams) are fully consistent with results of eddy-resolving simulations conducted for natural river confluences (e.g. Horna-Munoz et al 2020;Jiang et al 2022). A better alternative to using information from aerial photographs to characterize mixing at confluences with strong density contrast between the incoming streams may be the use of acoustic backscatter to characterize density variation over the flow depth.…”

Section: Volume Of Mixed Fluidsupporting

confidence: 88%

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Shallow mixing interfaces between parallel streams of unequal densities

Cheng

Constantinescu²

2022

J. Fluid Mech.

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As opposed to the case of shallow mixing layers forming between parallel streams of unequal velocities and equal densities, the spatial development of the mixing interface (MI) between two parallel streams of unequal velocities and sufficiently large density contrast is controlled by the formation of a spatially developing, lock-exchange-like flow in transverse planes. Buoyancy effects are driven by the presence of a vertical density interface near the splitter plate. Eddy-resolving numerical simulations conducted in a wide and very long channel are used to investigate the mean flow structure and the effects of the lock-exchange-like flow and the associated coherent structures on mixing and the capacity of the flow to entrain sediment from the channel bed. When the two streams have unequal densities, quasi-two-dimensional Kelvin–Helmholtz (KH) vortices still form near the MI origin, but their coherence is lost over a much shorter distance compared with the case with no density contrast, and their cores are severely stretched in the transverse direction. A main cell of recirculating (cross-) flow forms in the mean flow, in between the fronts of the near-bed intrusion of heavier fluid and the free-surface intrusion of lighter fluid. The instantaneous flow fields contain streamwise-oriented vortical cells along the interface separating the regions containing heavier and lighter fluids. These vortical cells play an important role in enhancing mixing, similar to the KH billows forming in a classical lock-exchange flow. The regions of highest turbulence amplification are situated next to the boundaries of the main recirculating cell. Once the oscillating fronts of the intrusions get sufficiently close to the channel sidewalls, streamwise cells of secondary flow form near the channel boundaries. For cases with a strong density contrast, the free-surface mixing pattern is not a good indicator of mixing between the two streams. For the same flow velocities in the incoming channels, the two streams mix faster with increasing density difference between the two streams. This is because, as opposed to the KH vortices, coherent structures induced by the formation of the lock-exchange-like flow maintain their coherence and capacity to induce mixing at very large distances from the splitter plate. Meanwhile, the redistribution of the streamwise momentum leading to uniform, fully developed flow over the whole cross-section is delayed by buoyancy effects. Away from the splitter plate, the region with the highest sediment entrainment potential is situated next to the edge of the main recirculation cell on the high-speed side of the channel. For the same flow velocities in the incoming channels, the sediment entrainment capacity of the flow is much larger in the simulations conducted with density contrast between the incoming streams and peaks for the case when the faster stream contains the denser fluid.

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Section: Volume Of Mixed Fluidsupporting

confidence: 88%

“…2020; Jiang et al. 2022). A better alternative to using information from aerial photographs to characterize mixing at confluences with strong density contrast between the incoming streams may be the use of acoustic backscatter to characterize density variation over the flow depth.…”

Section: Volume Of Mixed Fluidmentioning

confidence: 99%

Shallow mixing interfaces between parallel streams of unequal densities

Cheng

Constantinescu²

2022

J. Fluid Mech.

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“…(2020)) those authors describe a case with a F D = 4.9 as having “weak density effects” and one with F D = 1.6 as “strong density effects.” Thus, a value of F D of 5.2 is considered significant by Jiang et al. (2022), yet a similar value of 4.9 is considered weak by Horna‐Munoz et al. (2020).…”

Section: Discussionmentioning

confidence: 99%

“…The ensuing confusion is best illustrated with a recent excerpt from the literature. Jiang et al (2022) state: "Given that the corresponding densimetric Froude number (F D = 1/Ri 0.5 = 5.2) is less than 10, one expects density contrast effects to be fairly significant (Horna-Munoz et al, 2020) (p. 7)."…”

Section: Densimetric Froude Conventionsmentioning

confidence: 99%

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Impact of Density Gradients on the Secondary Flow Structure of a River Confluence

Duguay

Biron

Lacey

2022

Water Resources Research

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A greater understanding of these structures is therefore of obvious interest. Four structures are often discussed: helical cells (secondary flow at the scale of the tributaries' widths), vertically orientated Kelvin-Helmholtz (KH) vortices (shear-induced instabilities along the mixing interface), episodic pulses (origins still not fully understood, see Sabrina et al. (2021)) and streamwise orientated vortices (SOVs). SOVs were first discovered in numerical models as a pair of back-to-back, counter-rotating SOVs flanking each side of the mixing interface (Constantinescu et al., 2011) and their development is generally attributed to the downwelling of superelevated water, in a process strengthened by planform curvature (Sukhodolov & Sukhodolova, 2019). Recently, however strongly coherent SOVs were directly observed in turbidity currents at the Coaticook-Massawippi confluence (Duguay et al., 2022), and numerical modeling showed these SOVs to be gravity currents, caused by a small density gradient Δρ of ≈0.5 kg/m 3 , being confined between the converging flows (Duguay et al., 2022). Gaining knowledge of how greater magnitudes of Δρ and/or a reversal in the direction of Δρ influence these SOVs is the first step towards a full understanding of these intriguing flow structures.Density gradients develop when differences in temperature, dissolved minerals, or suspended sediment concentrations are present across the mixing interface. Density gradients commonly occur (

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Hydrogeomorphology of the origin of the Amazon River, the confluence between the Marañón and Ucayali rivers

Guerrero,

Abad,

Ortals

et al. 2024

Earth Surf Processes Landf

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The origin of the Amazon River is formed at the confluence of the Marañón and Ucayali rivers. Remote sensing and detailed hydrodynamics, sediment transport and bed morphology analysis under different hydrological conditions have been applied to understand the control mechanisms of the modern confluence, thus informing about ancient confluences. Results showed that: 1) meandering‐meandering confluences existed when bifurcated meandering channels from the Marañón River joined the meandering Ucayali River, 2) far‐field scale provided the boundary conditions for the near‐field scale processes. In the case of the Marañón River, the spatial frequency and displacement of incoming anabranching structures to the confluence location set the boundary conditions for the near‐field scale. In the case of the Ucayali River, the incoming hydrodynamics and bed morphology are governed by far‐field processes such as the occurrence of cutoffs, 3) high intensity secondary flows at large rivers were observed at far‐ and near‐field scales, where previous studies have reported that secondary flows are weak or nonexistence or mainly found downstream of confluences. Finally, 4) even though the Marañón River is larger compared with the Ucayali River, the confluence hydrogeomorphology is governed by the Ucayali River because of more developed and stronger secondary flows.

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Flow hydrodynamics, density contrast effects and mixing at the confluence between the Yangtze River and the Poyang Lake channel

Cited by 17 publications

References 65 publications

Shallow mixing interfaces between parallel streams of unequal densities

Shallow mixing interfaces between parallel streams of unequal densities

Impact of Density Gradients on the Secondary Flow Structure of a River Confluence

Hydrogeomorphology of the origin of the Amazon River, the confluence between the Marañón and Ucayali rivers

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