Impact of the Relative Submergence on Turbulence Structures in Open‐Channel Flow Through Arrays of Large Spherical Roughness Elements
Abstract This study investigates the impact of relative submergence, defined as the ratio of water depth to the diameter of boulders (k = H/D), on turbulence structures in flow through boulder arrays. The large‐eddy simulation method is employed to simulate flow through boulder arrays across a range...
Saved in:
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Wiley
2025-06-01
|
| Series: | Water Resources Research |
| Subjects: | |
| Online Access: | https://doi.org/10.1029/2024WR038282 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| _version_ | 1849421496210948096 |
|---|---|
| author | Zhengdao Tang Thorsten Stoesser Lei Huang Yan Liu Hongwei Fang |
| author_facet | Zhengdao Tang Thorsten Stoesser Lei Huang Yan Liu Hongwei Fang |
| author_sort | Zhengdao Tang |
| collection | DOAJ |
| description | Abstract This study investigates the impact of relative submergence, defined as the ratio of water depth to the diameter of boulders (k = H/D), on turbulence structures in flow through boulder arrays. The large‐eddy simulation method is employed to simulate flow through boulder arrays across a range of k values from 0.25 to 3.50. Within this range, three distinct flow regimes are identified: low (k = 0.25), intermediate (k = 0.75 and 1.25), and high (k = 2.0 and 3.5) relative submergence regimes. Across these three regimes, distributions of time‐averaged velocities, secondary flow, turbulent kinetic energy, and dominant turbulence structures in the wakes of boulders exhibit significant variations. The wake of boulders, characterized by recirculation flow, only manifests at k ≥ 0.75 and is more pronounced at higher k values. Particularly at k = 3.5, funnel vortices in the wake and secondary flow at the sides of boulders develop, enhancing vertical momentum exchange. Three types of coherent structures are identified within the wake: (a) the near‐bed hairpin vortex with a wavelength (λ) of 0.8D at the lowest k, (b) the lateral flapping of boulder wakes with λ=2.1D intermediate k, and (c) the meandering of high‐speed streaks at the side of boulders with λ=10D at high k. These structures alter the distribution of the near‐bed Reynolds shear stresses (RSS) and contribute up to 20% of the near‐bed RSS. At k ≤ 1.25, a region of low near‐bed shear stress appears upstream of boulders, while it shifts to the wake of boulders at k = 3.5, contributing the observed variations in deposition patterns at different k values as reported by Papanicolaou et al. (2018, https://doi.org/10.1029/2018jf004753). In addition, the two bedload periodicities reported in the experiment of Papanicolaou et al. (2018, https://doi.org/10.1029/2018jf004753) are justified by the ratio of the wavelength of lateral flapping of boulder wakes to that of meandering of low‐ and high‐speed streaks. |
| format | Article |
| id | doaj-art-76cc0e93bfd841069aa6af26eae5b4e0 |
| institution | Kabale University |
| issn | 0043-1397 1944-7973 |
| language | English |
| publishDate | 2025-06-01 |
| publisher | Wiley |
| record_format | Article |
| series | Water Resources Research |
| spelling | doaj-art-76cc0e93bfd841069aa6af26eae5b4e02025-08-20T03:31:27ZengWileyWater Resources Research0043-13971944-79732025-06-01616n/an/a10.1029/2024WR038282Impact of the Relative Submergence on Turbulence Structures in Open‐Channel Flow Through Arrays of Large Spherical Roughness ElementsZhengdao Tang0Thorsten Stoesser1Lei Huang2Yan Liu3Hongwei Fang4Department of Environmental Science and Engineering Southern University of Science and Technology Shenzhen ChinaDepartment of Civil, Environmental and Geomatic Engineering University College London London UKDepartment of Hydraulic Engineering Tsinghua University Beijing ChinaDepartment of Environmental Science and Engineering Southern University of Science and Technology Shenzhen ChinaDepartment of Hydraulic Engineering Tsinghua University Beijing ChinaAbstract This study investigates the impact of relative submergence, defined as the ratio of water depth to the diameter of boulders (k = H/D), on turbulence structures in flow through boulder arrays. The large‐eddy simulation method is employed to simulate flow through boulder arrays across a range of k values from 0.25 to 3.50. Within this range, three distinct flow regimes are identified: low (k = 0.25), intermediate (k = 0.75 and 1.25), and high (k = 2.0 and 3.5) relative submergence regimes. Across these three regimes, distributions of time‐averaged velocities, secondary flow, turbulent kinetic energy, and dominant turbulence structures in the wakes of boulders exhibit significant variations. The wake of boulders, characterized by recirculation flow, only manifests at k ≥ 0.75 and is more pronounced at higher k values. Particularly at k = 3.5, funnel vortices in the wake and secondary flow at the sides of boulders develop, enhancing vertical momentum exchange. Three types of coherent structures are identified within the wake: (a) the near‐bed hairpin vortex with a wavelength (λ) of 0.8D at the lowest k, (b) the lateral flapping of boulder wakes with λ=2.1D intermediate k, and (c) the meandering of high‐speed streaks at the side of boulders with λ=10D at high k. These structures alter the distribution of the near‐bed Reynolds shear stresses (RSS) and contribute up to 20% of the near‐bed RSS. At k ≤ 1.25, a region of low near‐bed shear stress appears upstream of boulders, while it shifts to the wake of boulders at k = 3.5, contributing the observed variations in deposition patterns at different k values as reported by Papanicolaou et al. (2018, https://doi.org/10.1029/2018jf004753). In addition, the two bedload periodicities reported in the experiment of Papanicolaou et al. (2018, https://doi.org/10.1029/2018jf004753) are justified by the ratio of the wavelength of lateral flapping of boulder wakes to that of meandering of low‐ and high‐speed streaks.https://doi.org/10.1029/2024WR038282relative submergenceboulder arrayshydrodynamicsopen channel flowturbulence structuressediment deposition |
| spellingShingle | Zhengdao Tang Thorsten Stoesser Lei Huang Yan Liu Hongwei Fang Impact of the Relative Submergence on Turbulence Structures in Open‐Channel Flow Through Arrays of Large Spherical Roughness Elements Water Resources Research relative submergence boulder arrays hydrodynamics open channel flow turbulence structures sediment deposition |
| title | Impact of the Relative Submergence on Turbulence Structures in Open‐Channel Flow Through Arrays of Large Spherical Roughness Elements |
| title_full | Impact of the Relative Submergence on Turbulence Structures in Open‐Channel Flow Through Arrays of Large Spherical Roughness Elements |
| title_fullStr | Impact of the Relative Submergence on Turbulence Structures in Open‐Channel Flow Through Arrays of Large Spherical Roughness Elements |
| title_full_unstemmed | Impact of the Relative Submergence on Turbulence Structures in Open‐Channel Flow Through Arrays of Large Spherical Roughness Elements |
| title_short | Impact of the Relative Submergence on Turbulence Structures in Open‐Channel Flow Through Arrays of Large Spherical Roughness Elements |
| title_sort | impact of the relative submergence on turbulence structures in open channel flow through arrays of large spherical roughness elements |
| topic | relative submergence boulder arrays hydrodynamics open channel flow turbulence structures sediment deposition |
| url | https://doi.org/10.1029/2024WR038282 |
| work_keys_str_mv | AT zhengdaotang impactoftherelativesubmergenceonturbulencestructuresinopenchannelflowthrougharraysoflargesphericalroughnesselements AT thorstenstoesser impactoftherelativesubmergenceonturbulencestructuresinopenchannelflowthrougharraysoflargesphericalroughnesselements AT leihuang impactoftherelativesubmergenceonturbulencestructuresinopenchannelflowthrougharraysoflargesphericalroughnesselements AT yanliu impactoftherelativesubmergenceonturbulencestructuresinopenchannelflowthrougharraysoflargesphericalroughnesselements AT hongweifang impactoftherelativesubmergenceonturbulencestructuresinopenchannelflowthrougharraysoflargesphericalroughnesselements |