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

Abstract

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 ≤ Φ = Nd2/D2 ≤ 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 Φ ≥ 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 Φ; (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 (StD) in the power spectrum of the lateral velocity, varying from 0.1614 to 0.1913.