Comparison of Turbulent Hydrodynamics with and without Emergent and Sparse Vegetation Patch in Free Surface Flow

Abstract

In the present study, we have compared the turbulent hydrodynamics in open turbulent flow with and without an emergent and sparse vegetation patch. The rigid patch, located at the middle cross-sectional region, was made by acrylic cylindrical rods with regular spacing between them along streamwise and transverse directions. The measurements of flow velocity components were taken by a Nortek Vectrino Plus acoustic Doppler velocimeter, and experimental data were collected along cross section for vegetation-free fully developed flow and along the cross section which is located at the middle of the streamwise length of the vegetation patch. Inside the vegetation patch, we have observed decreased value of time-averaged streamwise velocity in comparison with those of the vegetation-free fully developed flow. The time-averaged values of transverse and vertical velocities show increased magnitude with respect to the corresponding values in the vegetation-free fully developed flow. Inside the vegetation patch, with increasing transverse length from right-hand sidewall to left-hand sidewall, the magnitudes of normal stresses gradually increase and exceed the corresponding magnitudes of normal stresses in the vegetation-free fully developed flow. Along the cross section inside the patch, the magnitudes of governing Reynolds shear stress are smaller than the corresponding values of Reynolds shear stress without the vegetation. Along the cross section inside the patch, the vectors of secondary current follow are directed towards the left-hand sidewall together with zigzag pattern in vertical direction. In the interior of the vegetation, the strength of anticlockwise vortex in terms of the magnitude of moment of momentum is greater than that of the vegetation-free fully developed flow.