Dynamics of Turbulence in Low-Speed Oscillating Bottom-Boundary Layers of Stratified Basins |
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Authors: | Lorke Andreas Umlauf Lars Jonas Tobias Wüest Alfred |
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Institution: | (1) Applied Aquatic Ecology (APEC), Limnological Research Center, EAWAG, Kastanienbaum, Switzerland;(2) Departement de Génie Civil (DGC), Ecole Polytechnique Fédéral de Lausanne (EPFL), Lausanne, Switzerland |
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Abstract: | This paper focuses on the impact of an oscillating low-speed current on the structure and dynamics of the bottom-boundary layer (BBL) in a small stratified basin. A set of high-resolution current profile measurements in combination with temperature-microstructure measurements were collected during a complete cycle of the internal oscillation (`seiching') in the BBL of Lake Alpnach, Switzerland. It was found that even a relatively long seiching period of 24 hours significantly changed the form of the near-bottom current profiles as well as the dynamics of the turbulent dissipation rate compared to the steady-state law-of-the-wall. A logarithmic fit to the measured current profiles starting at a distance of 0.5 m above the sediment led to inconsistent estimates of both friction velocity and roughness length. Moreover, a phase lag between the current and the turbulent dissipation of 1.5 hours and a persistent maximum in the current profile at a height of 2.5 to 3 m above the sediment were observed. The experimental findings were compared to the results of a k- turbulence model and showed good agreement in general. Specifically, the inconsistent logarithmic fitting results and the observed phase lag were reproduced well by the model. |
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Keywords: | bottom-boundary layer dissipation rate k- model" target="_blank">gif" alt="epsi" align="BASELINE" BORDER="0"> model lake phase lag temperature microstructure turbulence |
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