Influence of surface roughness of dune bedforms on flow and turbulence characteristics |
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| Institution: | 1. Istanbul Technical University, Department of Civil Engineering, Maslak, Istanbul, 34469, Turkey;2. Department of Civil Engineering, Ahar Branch Islamic Azad University, Ahar, Iran;3. Division of Hydraulics, Department of Civil Engineering, University of Tabriz, Tabriz, Iran;1. Department of Civil Engineering, National Defense Academy, Japan;2. Université Grenoble Alpes, Laboratoire 3SR (sols, Solides, Structures, Risques), UMR 5521, Domaine Universitaire, BP53, France;1. State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin (SKL-WAC), Beijing 100048, China;2. China Institute of Water Resources and Hydropower Research (IWHR), Beijing 100048, China;3. Institute of Disaster Prevention, Beijing 101601, China;1. State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin (SKL-WAC), Beijing, China;2. China Institute of Water Resources and Hydropower Research (IWHR), Beijing, China;3. Surveying Design and Research Institute of Yellow River Henan Province, Zhengzhou, China;4. Jingjiang Bureau of Hydrology and Water Resources Survey, Changjiang Water Resources Commission, Jingzhou, China;1. Center for Mathematical Science and Advanced Technology, JAMSTEC, Yokohama, Japan;2. Plateforme de Constructions Hydrauliques, EPFL, Lausanne, Switzerland;3. Laboratory of Food Process Engineering, ETH, Zurich, Switzerland;4. Headquarters, JAMSTEC, Yokohama, Japan;1. Department of Water Engineering, Isfahan University of Technology, Isfahan, Iran;2. Environmental Engineering Program, University of Northern British Columbia 3333 University Way, Prince George British Columbia, Canada;1. Department of Civil Engineering, College of Engineering & Applied Sciences, Stony Brook University, Stony Brook, NY, USA;2. Department of Civil and Environmental Engineering, Hanyang University, Seoul, South Korea |
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| Abstract: | The current paper investigates the flow and turbulence characteristics over dune bedforms by means of laboratory experiments, where spatially dense and temporally high frequency velocity measurements were done. Although similar studies are available in the literature, the focus and novelty of the current study is to assess the influence of surface roughness of the dune bedforms on the nearbed flow. For direct comparison, two different surface roughness heights over idealized, fixed-shaped, high-angled dune bedforms were tested; one with a hydraulically-smooth surface, and the other with a fully-rough surface. Spatial variation of time-averaged flow as well as turbulence statistics were examined, which was complemented by streamline plots and spectral analyses. The results are interpreted from sediment entrainment and sediment transport points of view. The results show that increased dune surface roughness reduces the nearbed flow velocity, but increases the flow velocities at upper regions. The upward directed flow near the dune crests becomes stronger in the case of smooth surface, while the re-attachment point moves further downstream compared to the rough wall case. It is concluded that the roughness of the dune surface affects the nearbed flow and turbulence characteristics qualitatively and quantitatively, which is shown to have direct consequences on sediment entrainment characteristics. |
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| Keywords: | Bedforms Dunes Friction drag Turbulence Grain roughness Form drag |
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