Large Eddy Simulation of Turbulent Flow Through Submerged Vegetation

Large Eddy Simulations (LES) are performed for an open channel flow through idealized submerged vegetation with a water depth (h) to plant height (h (p)) ratio of h/h (p) = 1.5 according to the experimental configuration of Liu et al. (J Geophys Res Earth Sci, 2008). They used a 1D laser Doppler velocimeter (LDV) to measure longitudinal and vertical velocities as well as turbulence intensities along several verticals in the flow and the data are used for the validation of the present simulations. The code MGLET is used to solve the filtered Navier-Stokes equations on a Cartesian non-uniform grid. In order to represent solid objects in the flow, the immersed boundary method is employed. The computational domain is idealized with a box containing 16 submerged circular cylinders and periodic boundary conditions are applied in both longitudinal and transverse directions. The predicted streamwise as well as vertical mean velocities are in good agreement with the LDV measurements. Furthermore, fairly good agreement is found between calculated and measured streamwise and vertical turbulence intensities. Large-scale flow structures of different shapes are present in the form of vortex rolls above the vegetation tops as well as locally generated trailing and von- Karman-type vortices due to flow separation at the free end and the sides of the cylinders. In this paper, the flow field is analyzed statistically and evidence is provided for the existence of these structures based on the LES.