3-D turbulent structures in partly vegetated open-channel flows

The effects of the vegetation growing in the water and at the edge of water on the turbulent structures are not so clear as yet, in spite of their importance. In this study, the turbulence measurements of open-channel flows with vegetated zone at a half channel width were conducted by making use of a laser Doppler anemometer(LDA). It was found that the intensity of the secondary currents and the turbulence energy increase with an increase of the Froude numbers. The turbulence is advected Spanwisely near the free surface by the secondary currents, which are generated by the surface vortices. The horizontal vortices near the free surface are generated by the shear instability which increases with an increase of the Froude numbers. The wall shear stress in the vegetated zone is calculated by the equation of motion with the aid of the empirical drag coefficient.