Characteristics of the flow structures through and around a submerged canopy patch

The flow around submerged canopy patches with finite sizes plays a critical role in the sediment deposition and vegetation evolution. In this study, the submerged canopy patch was modeled as a porous array with a diameter D and a height h consisting of N rigid cylinder elements with a diameter d and exposed to a fully developed turbulent open channel flow with a depth H. High-resolution numerical simulations were conducted to investigate the effects of array density (0.021 <= Phi =Nd-2/D-2 <= 1) on mean and instantaneous flow fields and three-dimensional coherent structures by fixing the aspect ratio h/D at 1 and the submergence H/h at 2. The results showed that as the array became denser, the streamwise bleeding flow decreased while the lateral and vertical bleeding flow increased. When Phi >= 0.098, the group behavior of the array became significant: (1) a vertical shear layer was formed at the top of the array, and the downflow behind the array increased with Phi; (2) horseshoe vortex systems formed around the upstream base of the array; and (3) although no patch-scale vortex shedding was observed in the vorticity field in all simulated cases, there was a dominant dimensionless frequency (St(D)) in the power spectrum of the lateral velocity, varying from 0.1614 to 0.1913.

Automated summary

This study investigated the effects of submerged canopy patches on flow fields and the impact of array density on flow structure and coherent structures. Increasing array density led to a decrease in streamwise bleeding flow and an increase in lateral and vertical bleeding flow, with significant group behavior observed in the array.