Experimental and Numerical Analysis of Side Weir Flows in a Converging Channel

This paper investigates the lateral outflow over a short-crested side weir inserted in a converging rectangular channel with linearly decreasing width in the flow direction. This type of overflow device induces a spatially varied free-surface flow with decreasing discharge and, because of the convergent geometry, it can potentially improve the performance of the distribution channels commonly used in irrigation systems, sewer networks, wastewater plants, and hydropower facilities for flow diversion and control and for flood protection. A laboratory investigation is carried out to analyze the main hydraulic characteristics of this kind of flow and assess the improvement in outflow efficiency compared to the conventional rectangular side weir in a prismatic channel. Only subcritical steady flow conditions are considered. Experimental data show that the Froude number in the main channel downstream of the weir and the dimensionless weir height are significant variables to describe the outflow efficiency, and they confirm that the nonprismaticity of the main channel induces a noticeable increase in outflow performance. Furthermore, the experimental results show that the assumption of constant specific energy usually adopted in one-dimensional side weir flow modeling is reasonably valid, despite the considerable increase in the velocity-head and momentum correction coefficients along the side weir. Finally, the comparison between experimental data and numerical results shows that the classic one-dimensional modeling approach can adequately predict the main engineering aspects of side weir flows in nonprismatic channels.