Large eddy simulation of a long asymmetric compound open channel

A detailed Large Eddy Simulation of turbulent flow in a long compound open channel with one floodplain is reported. The Reynolds number is approximately 42,000 and the free surface was treated as fully deformable. The results are in agreement with experimental measurements and support the use of high spatial resolution and a large box length in contrast with a previous simulation of the same geometry. Details are reported of the time-varying floodplain flow and flow at the junction of the channel and the floodplain. A secondary flow is identified at the internal corner that persists and increases the bed stress on the floodplain. This phenomenon results from the lateral momentum transfer from the main channel by the extended secondary circulation existing in the interface region. This transfer of fluid is dominated by the relatively intense vorticity generated at the interface wall and corner. The regions of highest turbulent activity are elongated streaks near the walls that are aligned with the mean flow.