Buoyancy‐Tilted Shear Layers and Coherent Structures in Hyperpycnal River Plume Plunging
Abstract Shear layers and corresponding Kelvin Helmholtz‐type Coherent Structures (KHCS) can be generated by rivers discharging into laterally‐unconfined quiescent open water bodies (e.g., lakes). When the river discharge has a greater density than the receiving water due to temperature and/or suspe...
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2025-06-01
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| Online Access: | https://doi.org/10.1029/2024WR039696 |
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| author | H. Shi M. E. Negretti J. Chauchat K. Blanckaert U. Lemmin D. A. Barry |
| author_facet | H. Shi M. E. Negretti J. Chauchat K. Blanckaert U. Lemmin D. A. Barry |
| author_sort | H. Shi |
| collection | DOAJ |
| description | Abstract Shear layers and corresponding Kelvin Helmholtz‐type Coherent Structures (KHCS) can be generated by rivers discharging into laterally‐unconfined quiescent open water bodies (e.g., lakes). When the river discharge has a greater density than the receiving water due to temperature and/or suspended sediment, both the shear layers and KHCS will be influenced by the negative buoyancy of the plume and thus become highly three‐dimensional (3D). The present study uses a turbulence‐resolving Computational Fluid Dynamics model based on Large Eddy Simulation to simulate the nearshore flow fields of a hyperpycnal river plume entering an unconfined quiescent ambient. Shear layers are observed at both sides of the plume and their growth is suppressed by negative buoyancy arising from the greater density of the river plume. The plume‐ambient interface is tilted by the negative buoyancy and is transformed into a curved face. As a result, the shear layer is also tilted and shear‐induced vorticity progressively changes its direction from vertical near the water surface to transversal near the bottom. Tilted along with the shear layers, KHCS present unique 3D subsurface structures and create strongly mixed and curved “coherent structure regions” in transects. Quadrant analysis shows that the “Ejection” and “Sweep” events associated with KHCS dominate the local mass and momentum exchange between the plume and ambient water. At the plume‐ambient interface, the KHCS generate near‐periodic velocity fluctuations whose non‐dimensionalized frequency (Strouhal number) decreases with increasing local Richardson number. |
| format | Article |
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| issn | 0043-1397 1944-7973 |
| language | English |
| publishDate | 2025-06-01 |
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| series | Water Resources Research |
| spelling | doaj-art-ab947b1cf93c476187812528077de16f2025-07-04T11:51:25ZengWileyWater Resources Research0043-13971944-79732025-06-01616n/an/a10.1029/2024WR039696Buoyancy‐Tilted Shear Layers and Coherent Structures in Hyperpycnal River Plume PlungingH. Shi0M. E. Negretti1J. Chauchat2K. Blanckaert3U. Lemmin4D. A. Barry5School of Ocean Sciences Bangor University Menai Bridge Anglesey UKUniversité Grenoble Alpes CNRS Grenoble INP LEGI UMR 5519 Grenoble FranceUniversité Grenoble Alpes CNRS Grenoble INP LEGI UMR 5519 Grenoble FranceResearch Unit Hydraulic Engineering and Environmental Hydromechanics Institute of Hydraulic Engineering and Water Resources Management Technische Universität Wien Vienna AustriaEcological Engineering Laboratory (ECOL), Environmental Engineering Institute (IIE), Faculty of Architecture, Civil and Environmental Engineering (ENAC) École Polytechnique Fédérale de Lausanne (EPFL) Lausanne SwitzerlandEcological Engineering Laboratory (ECOL), Environmental Engineering Institute (IIE), Faculty of Architecture, Civil and Environmental Engineering (ENAC) École Polytechnique Fédérale de Lausanne (EPFL) Lausanne SwitzerlandAbstract Shear layers and corresponding Kelvin Helmholtz‐type Coherent Structures (KHCS) can be generated by rivers discharging into laterally‐unconfined quiescent open water bodies (e.g., lakes). When the river discharge has a greater density than the receiving water due to temperature and/or suspended sediment, both the shear layers and KHCS will be influenced by the negative buoyancy of the plume and thus become highly three‐dimensional (3D). The present study uses a turbulence‐resolving Computational Fluid Dynamics model based on Large Eddy Simulation to simulate the nearshore flow fields of a hyperpycnal river plume entering an unconfined quiescent ambient. Shear layers are observed at both sides of the plume and their growth is suppressed by negative buoyancy arising from the greater density of the river plume. The plume‐ambient interface is tilted by the negative buoyancy and is transformed into a curved face. As a result, the shear layer is also tilted and shear‐induced vorticity progressively changes its direction from vertical near the water surface to transversal near the bottom. Tilted along with the shear layers, KHCS present unique 3D subsurface structures and create strongly mixed and curved “coherent structure regions” in transects. Quadrant analysis shows that the “Ejection” and “Sweep” events associated with KHCS dominate the local mass and momentum exchange between the plume and ambient water. At the plume‐ambient interface, the KHCS generate near‐periodic velocity fluctuations whose non‐dimensionalized frequency (Strouhal number) decreases with increasing local Richardson number.https://doi.org/10.1029/2024WR039696hyperpycnal river plumenegative buoyancyshear layerKelvin Helmholtz‐type coherent structures |
| spellingShingle | H. Shi M. E. Negretti J. Chauchat K. Blanckaert U. Lemmin D. A. Barry Buoyancy‐Tilted Shear Layers and Coherent Structures in Hyperpycnal River Plume Plunging Water Resources Research hyperpycnal river plume negative buoyancy shear layer Kelvin Helmholtz‐type coherent structures |
| title | Buoyancy‐Tilted Shear Layers and Coherent Structures in Hyperpycnal River Plume Plunging |
| title_full | Buoyancy‐Tilted Shear Layers and Coherent Structures in Hyperpycnal River Plume Plunging |
| title_fullStr | Buoyancy‐Tilted Shear Layers and Coherent Structures in Hyperpycnal River Plume Plunging |
| title_full_unstemmed | Buoyancy‐Tilted Shear Layers and Coherent Structures in Hyperpycnal River Plume Plunging |
| title_short | Buoyancy‐Tilted Shear Layers and Coherent Structures in Hyperpycnal River Plume Plunging |
| title_sort | buoyancy tilted shear layers and coherent structures in hyperpycnal river plume plunging |
| topic | hyperpycnal river plume negative buoyancy shear layer Kelvin Helmholtz‐type coherent structures |
| url | https://doi.org/10.1029/2024WR039696 |
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