Parameterization of the logarithmic layer of double-averaged streamwise velocity profiles in gravel-bed river flows |
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Authors: | Mário J Franca Rui ML Ferreira Ulrich Lemmin |
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Institution: | 1. Department of Civil Engineering and IMAR-CMA, University of Coimbra, Pólo II, 3030-788 Coimbra, Portugal;2. Department of Civil Engineering and Architecture, Instituto Superior Técnico, TULisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal;3. Laboratoire d’Hydraulique Environnementale (LHE), École Polytechnique Fédérale de Lausanne, CH 1015 Lausanne, Switzerland |
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Abstract: | The logarithmic layer of double-averaged (in time and space) streamwise velocity profiles obtained from field measurements made in the Swiss rivers, Venoge and Chamberonne is parameterized and discussed. Velocity measurements were made using a 3D Acoustic Doppler Velocity Profiler. Both riverbeds are hydraulically rough, composed of coarse gravel, with relative submergences (h/D50) of 5.25 and 5.96, respectively. From the observations, the flow may be divided into three different layers: a roughness layer near the bed, an equivalent logarithmic layer and a surface or outer layer. It was found that a logarithmic law can describe the double-averaged profiles in the layer 0.30 < z/h < 0.75. The parameterization of the logarithmic law is discussed. Special emphasis is given to the geometric parameters roughness and zero-displacement heights and to the equivalent von Karman constant. |
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Keywords: | Double-averaged velocity profiles Logarithmic law Velocity field measurements |
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