Author(s): Taira Ozaki; Taisuke Ishigaki; Koji Shiono; Edgar Ferreira; Jim Chandler; Rene Wackrow
Linked Author(s): Taira Ozaki, Edgar Ferreira, Taisuke Ishigaki
Keywords: Open channel; Experiment; Trees; Turbulence; Flow structure
Abstract: There have been many emergent vegetation studies using cylindrical or squared rods for simulating real trees in open channel. Rods generate turbulent flow characteristics similar to those of tree trucks without branches and canopies, however when branches and canopies are included, they would be expected to be quite different. This paper therefore investigates turbulence behaviour in open channel with real trees, including canopies, in line along the channel. Experiments are conducted in a flume with miniature trees placed at the centre of the flume. Various arrangements of the tree spacing were performed. Turbulent measurements are undertaken by Acoustic Doppler Velocimetry (ADV). ADV measures three components of turbulent fluctuations, as a result mean velocities, turbulent kinetic energies and Reynolds stresses are obtained. Turbulent flow structure caused by trees is characterised by mean velocity, turbulent kinetic energy and Reynolds stress. The detailed mean velocities are shown at three cross sections behind the one tree and compared with those obtained by the wake theory. As for turbulent flow field, peaks of the turbulent kinetic energy and Reynolds stress for the one tree, two trees and three trees are observed and they are not immediately behind the trees. The locations of the maximum Reynolds stresses occurred are also observed and related to vortex shedding. Drag coefficients are estimated by the wake profile behind vegetation with the wake formula.
Year: 2013