Flow Characteristics in Partly Vegetated Channels: An Experimental Investigation

Abstract

In this study, we attempt to experimentally investigate the flow turbulence structure in a partly vegetated channel. To achieve the objective of this study, we conducted extensive measurements of flow velocities within and outside the vegetated area, where the flow is fully developed. The experiments were conducted in a very large channel at the Coastal Engineering Laboratory of the Department of Civil, Environmental, Building Engineering and Chemistry at the Polytechnic University of Bari, Italy. The instantaneous three flow velocity components were accurately measured using a 3D-Acoustic Doppler Velocimeter (ADV)-Vectrino system at high frequency. Flow behaviors through the vegetated area, at the interface, and in the unobstructed area were analyzed via time-averaged velocities, turbulence intensity, correlation properties, spectral analysis, and vortex identification. Experimental results showed the development of three distinct characteristic flow zones: (i) a vegetated area of low streamwise velocity, high turbulence intensities, dominant inward interactions, and more intense power spectrum, (ii) a shear layer zone of increasing streamwise velocity, more enhanced transverse flow motion, exponential decrease in turbulence intensities, and frequent ejection and/or outward interaction events, and (iii) a free-stream zone of higher and almost constant streamwise velocity, lower turbulence intensities, frequent sweep and/or inward interaction events, and less intense streamwise power spectrum. The results brought further insights into the flow behaviors in these characteristic flow zones. The extensive and detailed measured data can provide a basis for improving and calibrating numerical simulations of partly vegetated channels.