Tang, Zhengdao;
Stoesser, Thorsten;
Huang, Lei;
Liu, Yan;
Fang, Hongwei;
(2025)
Impact of the Relative Submergence on Turbulence Structures in Open-Channel Flow Through Arrays of Large Spherical Roughness Elements.
Water Resources Research
, 61
(6)
, Article e2024WR038282. 10.1029/2024WR038282.
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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 (Formula presented.) 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 ((Formula presented.)) of 0.8D at the lowest k, (b) the lateral flapping of boulder wakes with (Formula presented.) intermediate k, and (c) the meandering of high-speed streaks at the side of boulders with (Formula presented.) 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 (Formula presented.) 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.
| Type: | Article |
|---|---|
| Title: | Impact of the Relative Submergence on Turbulence Structures in Open-Channel Flow Through Arrays of Large Spherical Roughness Elements |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1029/2024WR038282 |
| Publisher version: | https://doi.org/10.1029/2024wr038282 |
| Language: | English |
| Additional information: | This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. See: http://creativecommons.org/licenses/by-nc/4.0/ |
| Keywords: | Science & Technology, Life Sciences & Biomedicine, Physical Sciences, Environmental Sciences, Limnology, Water Resources, Environmental Sciences & Ecology, Marine & Freshwater Biology, relative submergence, boulder arrays, hydrodynamics, open channel flow, turbulence structures, sediment deposition, ADV MEASUREMENTS, BOULDER ARRAY, BED, SIMULATION, TRANSPORT, HYDRAULICS, RESISTANCE, MODEL, LAYER |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Civil, Environ and Geomatic Eng |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10211372 |
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