How Different Cross-Sectional Shapes Influence the Separation Zone of an Open-Channel Confluence

A key feature of a schematized open-channel confluence is the separation zone that is present when the tributary flow detaches from the downstream corner of the confluence. This zone of recirculating fluid influences head losses, as well as sediment and solute balances. Most laboratory studies on the separation zone were, however, made in flumes having a rectangular cross-sectional shape. The objective of this research is therefore to elaborate on the influence of the cross-sectional shape on the flow patterns in a 90 degrees confluence. A validated large-eddy simulation (LES) model is used to study the flow in confluences with four different cross-sectional shapes. The results indicate that the dimensions of the separation zone are significantly different for nonrectangular shapes due to lateral currents that might reduce the local momentum deficit. This study contributes to finding the optimal shape of artificial confluences with respect to head losses, as well as to understanding the flow processes that are present in a confluence. (C) 2017 American Society of Civil Engineers.