Large Eddy Simulation of flow in a T-shaped open-channel bifurcation
Abstract
Open-channel bifurcations occur at river islands or delta-shaped mouths, and in engineered hydraulic systems, like water intakes and combined sewer overflows. The complex flow features are often studied experimentally or numerically at laboratory scale. In such systems, flow separation and recirculation strongly influence mass transport, mixing processes, and energy losses. This numerical study focuses on the detailed flow in a laboratory-scale bifurcation, making use of straight channels with rectangular cross-sections and concordant, fixed and smooth beds, where the lateral branch is perpendicular to the main channel, yielding an intersection with sharp edges. It is designed to replicate a flow configuration studied experimentally at INSA Lyon, where 3D particle tracking velocimetry revealed helical ascending trajectories within the recirculation region. The numerical model employs a Large Eddy Simulation (LES), wall functions, a synthetic turbulence generator at the inlet, and the Volume of Fluid (VoF) method to capture the free surface. The simulation reproduces junction flow features, including flow separation at the upstream junction corner and the formation of a recirculation zone in the lateral branch. Model performance is evaluated by comparison with the experimental data, including time-averaged velocity fields, streamlines, and the rotation centres at different elevations in the recirculation zone. The numerical results demonstrate the predictive capability of the present LES model. After verification whether a wall-resolved model version has a superior quality, the impact of Froude number and width-to-depth ratio on the flow features will be studied with the selected model version in future research.