Flow and sediment transport in shallow reservoirs : experimental and computational modelling

Abstract

Shallow reservoirs are used in many engineering applications. They can be optimized to trap sediments or inversely to store water. For the latest purpose, it is essential to minimize the sedimentation to preserve the initial storage capacity. Complex flows that develop in rectangular reservoirs were investigated and show a significant impact on sediments transport. However, only a few studies were focused on asymmetric geometries. The goal of this Master's thesis is to study the influence of entry angles of hexagons on asymmetric flow patterns. Real reservoir characteristics are used to increase the practical interest of this study.

This study uses the software Wold2D to numerically model several configurations, leading to new insights and conditions governing the flow. Experimental modeling in the hydraulic laboratory of ULiège aims to confirm the numerical results. Experiments also enable us to better understand some effects and to complete the numerical analyses.

One parameter including the angles is found to determine numerically the direction of the jet. Some of these results are confirmed experimentally. Experimental studies highlight the strong dependence of the flow on the initial conditions and the stability of both upwards and downwards directions of the jet for each configuration. Numerical relationships for the reattachment length are determined, but cannot be obtained experimentally due to high variability. The specific case of geometries with at least one inlet angle being smaller than approximately 30° is detailed numerically. The experimental results match expectations, but indicate an additional recirculation cell. In conclusion, the angles are shown to have a significant impact on the flow. It is therefore expected to modify the sedimentation. This hypothesis could be studied in future research.