Large-eddy simulation of turbulent rectangular open-channel flow with an emergent rigid vegetation patch

• The Large-eddy simulation (LES) was successfully used in this paper.
• A phenomenological model for spatial evolution of turbulent motions in vegetation flow decomposed the entire flow region into four zones.
• LES results provided insight into the spatial evolution of turbulent motions.
• The inter-connection between the lengths of the vortices and the scale of the vegetation elements were provided.

The turbulent structures caused by vegetation patch in open channel flows are generally poorly simulated in common turbulent models. Understanding the turbulent structures is essential to investigate important hydrodynamic processes taking place in aquatic ecosystems and fluvial environments. A Large-eddy simulation model is here developed to investigate the flow in a rectangular open channel partially blocked with an artificial emergent vegetation patch. We focus on the effects of turbulent structures on the momentum transfer across the outer line of vegetation region. The calculated results compared well with laboratory measurements. The spatial evolution of turbulent motions was analyzed, and the lengths of the vortices corresponding to the dominant frequency at different locations in the fully developed zone were investigated using a method of spectral analysis based on the model results. A phenomenological model was proposed for the evolution process in the vegetation flow, which divided the entire flow region into four zones: the initial flow zone, the diverging flow zone, the developing zone and the fully developed zone. Vortices at the inner side of the vegetation patch were mainly produced by the wake behind the vegetation element. Vortices in other locations were caused by the vegetation patch, which corresponded exactly to the turbulent structures owing to the interaction between flow and vegetation at the edge of the patch.