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Flow patterns and sediment deposition in rectangular shallow reservoirs ; Dewals, Benjamin ; Erpicum, Sébastien et al in Water & Environment Journal (2012), 26(4), 504-510 This work involves the experimental investigation of flow patterns, preferential regions of deposition and trapping efficiency in rectangular shallow reservoirs. The main flow patterns that can be ... [more ▼] This work involves the experimental investigation of flow patterns, preferential regions of deposition and trapping efficiency in rectangular shallow reservoirs. The main flow patterns that can be encountered in rectangular shallow reservoirs are described: symmetrical flows without any reattachment point (S0), asymmetrical flows with one reattachment point (A1), and asymmetrical flows with two reattachment points (A2). The influence of geometrical and hydraulic parameters on reattachment lengths is intensively investigated. A shape parameter is introduced to classify symmetrical and asymmetrical flows. For each flow pattern, the preferential regions of deposition are studied. To conclude, a number of practical recommendations are given. Reservoirs with a shape parameter lower than 6.2 limit sediment deposition. Reservoirs with a shape parameter greater than 6.8 are favourable for sediment deposition. Finally, perspectives for maximizing and minimizing deposition are given, respectively by exploiting the great trapping potential of the flow pattern A1 and the poor trapping potential of the flow pattern S0. [less ▲] Detailed reference viewed: 119 (32 ULg)Numerical investigation of flow patterns in rectangular shallow reservoirs ; Dewals, Benjamin ; Erpicum, Sébastien et al in Engineering Applications of Computational Fluid Mechanics (2011), 5(2), 247-258 The present work gives findings profitable for the person who wants to evaluate an asymmetric detach-reattach flow. In this study, the capability of a two-dimensional shallow-water numerical model to ... [more ▼] The present work gives findings profitable for the person who wants to evaluate an asymmetric detach-reattach flow. In this study, the capability of a two-dimensional shallow-water numerical model to simulate the symmetric and asymmetric flows that can take place in rectangular shallow reservoirs varying the lateral expansion ratio and the dimensionless length is investigated. For a large lateral expansion ratio, the use of two protocols of simulation highlighted a high sensitivity of the simulated flow pattern to the initial condition. Comparison between simulated results and experimental data showed a good agreement for the critical shape parameter (combination of the lateral expansion ratio and the dimensionless length) between symmetric and asymmetric flows. A good agreement was also found for the value of the shorter reattachment length of asymmetric flows. For small lateral expansion ratios, the agreement was not so good. The model was used for even larger lateral expansion ratios in order to numerically extend the experimental dataset. This predictive work showed that the shape parameter, whose expression was only based on experiments carried out for small lateral expansion ratios, was also relevant for larger values. Moreover, the predicted values of the shorter reattachment length were also consistent with a regression only based on experimental results. [less ▲] Detailed reference viewed: 202 (48 ULg)Experimental investigation of flow pattern and sediment deposition in rectangular shallow reservoirs ; Dewals, Benjamin ; Erpicum, Sébastien et al in International Journal of Sediment Research (2010), 25(3), 258-270 This work involved the experimental investigation of flow pattern, preferential regions of deposition and trap efficiency as a function of the length of rectangular shallow reservoirs. Four flow patterns ... [more ▼] This work involved the experimental investigation of flow pattern, preferential regions of deposition and trap efficiency as a function of the length of rectangular shallow reservoirs. Four flow patterns were identified (from longer to shorter reservoirs): an asymmetric flow with two reattachment points, an asymmetric flow with one reattachment point, an unstable flow, and a symmetric flow without any reattachment point. Using dye visualizations, the median value and the temporal variability of the reattachment lengths were precisely measured for the asymmetric flows. For each stable flow, sediment tests with plastic particles were carried out. The regions of deposition on the bed of the reservoir were clearly a function of the flow pattern. The transition from an asymmetric flow pattern to a symmetric flow pattern was responsible for an abrupt decrease of the trap efficiency; a number of regression laws were discussed to take it into account. [less ▲] Detailed reference viewed: 137 (44 ULg)Classification of flow patterns in rectangular shallow reservoirs ; Dewals, Benjamin ; Erpicum, Sébastien et al in Journal of Hydraulic Research (2010), 48(2), 197-204 This work focuses on the experimental classification of flow patterns in rectangular shallow reservoirs, including symmetric flows without any reattachment point to asymmetric flows with one reattachment ... [more ▼] This work focuses on the experimental classification of flow patterns in rectangular shallow reservoirs, including symmetric flows without any reattachment point to asymmetric flows with one reattachment point, two reattachment points, or two reattachment points and one detachment point. The median position and the natural variability of the reattachment lengths of asymmetric flows were measured for forty geometric and hydraulic conditions. The effects of dimensionless flow depth, Froude number, lateral expansion ratio and dimensionless length on the median reattachment lengths were analyzed. A number of regression equations were proposed. For “high” dimensionless flow depths and a Froude number of 0.20, a shape parameter was proposed for predicting the transition between symmetric and asymmetric flows. The results of this study are useful knowledge for improving current methods to predict the trapping efficiency and the preferential regions of deposition in reservoirs. [less ▲] Detailed reference viewed: 96 (42 ULg) |
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