Large eddy simulation of fully-developed turbulent flow through submerged vegetation

Large Eddy Simulations (LES) are performed for an open channel flow through submerged vegetation with a water depth (h) to plant height (h,) ratio of h/h(p) = 1.5 according to the experimental configuration of Fairbanks and Diplas (1998). Fairbanks and Diplas measured 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 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 four 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 LDA measurements. Furthermore, good agreement is found between calculated and measured streamwise r.m.s velocities. Large-scale flow structures of different shape are present in the form of vortex rolls above the vegetation tops as well as von Karman type vortices generated by flow separation at the cylinders. In this paper the mean and instantaneous flow field is analyzed and further insight into the complex nature of flow through vegetation is provided based on Large Eddy Simulation.