Flow and turbulence structure past a dense circular patch of vegetation

Wen-Yi Chang, George Constantinescu, Whey-Fone Tsai

Friday 3 july 2015

9:30 - 9:45h at North America (level 0)

Themes: (T) Hydro-environment, (ST) Ecohydraulics and ecohydrology

Parallel session: 14F. Environment - Ecohydraulic

In the present study, flow and turbulence structure past a circular patch of emerged vegetation containing a number of 250 identical circular rigid cylinders is investigated, corresponding to a solid volume fraction SVF=0.23. Similar to most previous laboratory studies of channels containing vegetation, the rigid plant stems are modeled as solid vertical cylinders of diameter d=0.03D disposed in a staggered arrangement, where D is the diameter of the porous cylinder. Eddy resolving simulations that resolve the large scale coherent structures are conducted at a Reynolds number of 20,000 defined with the channel depth h (h/D=0.45) and the bulk velocity of the fully developed incoming turbulent flow in the channel containing the patch are conducted for the porous cylinder case (SVF=0.23) and for the corresponding solid cylinder case (SVF=1.0). The flow past the individual cylinders (plant stems) is resolved. The paper discusses the changes in the structure of the mean flow and turbulence within the wake region, how the bleeding flow influences the large scale vortex shedding behind the cylinder and how the characteristics of the horseshoe vortex system forming around the upstream face of the cylinder change with the SVF. The bed friction velocity distributions that determine the capacity of the flow to entrain sediment within and around the patch are analyzed.