Effects of different porous beds on turbulent characteristics in an open channel above the porous bed

Abstract

An analysis of the turbulent characteristics of the flow in an open channel with horizontal porous beds using two-dimensional (2D) Particle Image Velocimetry (PIV) is presented. Hydraulic characteristics such as velocity distributions, turbulent intensities and Reynolds stress are investigated at a fine resolution using the PIV. Experiments were carried out, with four types of porous bed with the same porosity ε=0.70 and the same porous thickness (3cm): (a) porous filter, (b) rods bundle, (c) grass vegetation and (d) gravel bed. Turbulent characteristics are measured above the porous bed for the same different water heights (h΄=3, 5, 7 and 9cm) and for the same slope S=1.5‰. Main emphasis is given to the effects of relative porous thickness s΄/h (s΄=porous thickness, h=total flow height) on the flow characteristics over the porous beds. The relative thickness s΄/h varies between 0.250 and 0.500. The discharge ranges between 3.0 and 24.6 lt/s. Measurements of mean velocity and turbulence characteristics indicate the effects of the bed material used on the flow characteristics. The presence of rods bundle influences with different way the turbulent characteristics of the flow as regards the other porous beds.