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Effect of Relative Submergence on the Flow and Mass Exchange Processes in a Channel with Two Lateral Groynes

Author(s): Andrew Mccoy; George Constantinescu; Mete Koken; Larry Weber

Linked Author(s): George Constantinescu, Larry J. Weber

Keywords: No Keywords

Abstract: Large Eddy Simulation (LES) is used to study the flow dynamics around two groynes forming an embayment in a flat-bed open channel with lateral vertical walls. Additionally, the mass exchange processes between the embayment and the main channel are investigated by considering the ejection of a passive scalar introduced instantaneously inside the embayment. The interest in this configuration is motivated by its similarity to flow around groyne fields in natural rivers. Two cases are studied. In the first one the groynes are fully emerged corresponding to normal flow conditions in the channel. In the second one, the groynes are fully submerged and the ratio between the channel depth and the embayment depth is 1. 4, corresponding to flooding conditions (large relative submergence depth). The geometry, dimensions and position of the groynes, and the flow conditions are identical in the two cases. Compared to the emerged case, the hydrodynamics of the flow past submerged groynes is far more complicated and three-dimensional effects are considerably stronger because in addition to the horizontal detached shear layer which plays a similar role in both cases, there is a vertical detached shear layer associated with the flow over the top of the embayment. As a result of the overflow, it is found that important differences are present in the turbulent kinetic energy (TKE) distributions and those of various depth-averaged quantities between the emerged and submerged cases. The contaminant removal process is found to be faster in the submerged case because of the additional roof interface through which the contaminant can leave the embayment volume


Year: 2007

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