Time-averaged flow characterisations in a bimodal gravel-bed stream and relative role of sediment depositions on near-bed coherent flow structures
The present study aims to quantify experimentally the relative role of sediment depositions on near-bed flows and turbulence in a gravel-bed stream. Time-averaged velocity was measured over a sand-filled gravel-bed stream with four cases of sediment depositions and compared with those over a gravel-...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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IWA Publishing
2024-03-01
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| Series: | Water Supply |
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| Online Access: | http://ws.iwaponline.com/content/24/3/835 |
| _version_ | 1797200673451802624 |
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| author | Ratul Das Pritam Malakar Akash Datta |
| author_facet | Ratul Das Pritam Malakar Akash Datta |
| author_sort | Ratul Das |
| collection | DOAJ |
| description | The present study aims to quantify experimentally the relative role of sediment depositions on near-bed flows and turbulence in a gravel-bed stream. Time-averaged velocity was measured over a sand-filled gravel-bed stream with four cases of sediment depositions and compared with those over a gravel-bed stream without sediment depositions. An acoustic Doppler velocimeter was used to measure the instantaneous velocity of flows. The progressive infilling of void spaces in the gravel-bed stream forms distinct bimodal depositions that alter the mean flows characterised by increasing zero-velocity levels and massive damping in the bed shear stresses. The data plots of turbulent intensity depict enhancement of streamwise turbulent intensity in the near-bed flow region with increasing sand depositions. Moreover, the opposite nature of streamwise and vertical turbulent kinetic energy fluxes in the interfacial sublayer leads to slowing down the time-average Reynolds shear stresses at the vicinity of the gravel-bed surface. At the vicinity of the crest, the ejection and sweep events contributed approximately 86 and 56%, respectively, to the total Reynolds shear stress production in the case of gravel bed under clear-water flow conditions. By contrast, the contributions of turbulent sweep events increased over the sand-filled gravel bed at the same location.
HIGHLIGHTS
Sediment particle entrainment and interstices within the pore spaces of a gravel bed.;
Results are compared with the flows over an immobile gravel-bed stream under clear-water flow conditions.;
A higher level of sand deposition depicts massive damping in the near-bed Reynolds shear stress profiles.; |
| first_indexed | 2024-04-24T07:35:23Z |
| format | Article |
| id | doaj.art-a5331ca5dade45d38c312092b0a6af1a |
| institution | Directory Open Access Journal |
| issn | 1606-9749 1607-0798 |
| language | English |
| last_indexed | 2024-04-24T07:35:23Z |
| publishDate | 2024-03-01 |
| publisher | IWA Publishing |
| record_format | Article |
| series | Water Supply |
| spelling | doaj.art-a5331ca5dade45d38c312092b0a6af1a2024-04-20T06:36:17ZengIWA PublishingWater Supply1606-97491607-07982024-03-0124383584610.2166/ws.2024.027027Time-averaged flow characterisations in a bimodal gravel-bed stream and relative role of sediment depositions on near-bed coherent flow structuresRatul Das0Pritam Malakar1Akash Datta2 Department of Civil Engineering, National Institute of Technology Agartala, Tripura, 799046, India Civil Engineering Department, G. H. Raisoni University Amravati, Maharashtra 444701, India Department of Civil Engineering, National Institute of Technology Agartala, Tripura, 799046, India The present study aims to quantify experimentally the relative role of sediment depositions on near-bed flows and turbulence in a gravel-bed stream. Time-averaged velocity was measured over a sand-filled gravel-bed stream with four cases of sediment depositions and compared with those over a gravel-bed stream without sediment depositions. An acoustic Doppler velocimeter was used to measure the instantaneous velocity of flows. The progressive infilling of void spaces in the gravel-bed stream forms distinct bimodal depositions that alter the mean flows characterised by increasing zero-velocity levels and massive damping in the bed shear stresses. The data plots of turbulent intensity depict enhancement of streamwise turbulent intensity in the near-bed flow region with increasing sand depositions. Moreover, the opposite nature of streamwise and vertical turbulent kinetic energy fluxes in the interfacial sublayer leads to slowing down the time-average Reynolds shear stresses at the vicinity of the gravel-bed surface. At the vicinity of the crest, the ejection and sweep events contributed approximately 86 and 56%, respectively, to the total Reynolds shear stress production in the case of gravel bed under clear-water flow conditions. By contrast, the contributions of turbulent sweep events increased over the sand-filled gravel bed at the same location. HIGHLIGHTS Sediment particle entrainment and interstices within the pore spaces of a gravel bed.; Results are compared with the flows over an immobile gravel-bed stream under clear-water flow conditions.; A higher level of sand deposition depicts massive damping in the near-bed Reynolds shear stress profiles.;http://ws.iwaponline.com/content/24/3/835gravel bedinterfacial sublayerreynolds shear stresssand-filled gravel bedsweep eventsturbulence |
| spellingShingle | Ratul Das Pritam Malakar Akash Datta Time-averaged flow characterisations in a bimodal gravel-bed stream and relative role of sediment depositions on near-bed coherent flow structures Water Supply gravel bed interfacial sublayer reynolds shear stress sand-filled gravel bed sweep events turbulence |
| title | Time-averaged flow characterisations in a bimodal gravel-bed stream and relative role of sediment depositions on near-bed coherent flow structures |
| title_full | Time-averaged flow characterisations in a bimodal gravel-bed stream and relative role of sediment depositions on near-bed coherent flow structures |
| title_fullStr | Time-averaged flow characterisations in a bimodal gravel-bed stream and relative role of sediment depositions on near-bed coherent flow structures |
| title_full_unstemmed | Time-averaged flow characterisations in a bimodal gravel-bed stream and relative role of sediment depositions on near-bed coherent flow structures |
| title_short | Time-averaged flow characterisations in a bimodal gravel-bed stream and relative role of sediment depositions on near-bed coherent flow structures |
| title_sort | time averaged flow characterisations in a bimodal gravel bed stream and relative role of sediment depositions on near bed coherent flow structures |
| topic | gravel bed interfacial sublayer reynolds shear stress sand-filled gravel bed sweep events turbulence |
| url | http://ws.iwaponline.com/content/24/3/835 |
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