Experimental study of the effects of grass vegetation and gravel bed on the turbulent flow using particle image velocimetry

Abstract

Laboratory experiments are used to explore the effect of impermeable bed on the turbulent flow by using particle image velocimetry (PIV). The experiments were conducted in an open channel of 6.5 m length, 7.5 cm width and 25 cm height. Two different types of permeable bed (flexible vegetation with grass and gravel bed) with different height (2 and 6 cm) with the same porosity ϵ = 0.80 (volume of fluid over total porous medium volume) were used to represent the porous bed. These conditions can be commonly found in systems with sediment transport. Forty-eight (48) experiments were carried out for permeable beds, twenty-four (24) for flexible vegetation with grass and twenty-four (24) for gravel bed. Hydraulic characteristics such as distributions of velocities, turbulent intensities, turbulent kinetic energy and Reynolds stress are investigated. Measurements of velocity were taken for horizontal channel slope at different heights using the PIV. Results show that the kind of the bed type can significantly influence the turbulent characteristics of the flow.

Keywords:

• flow structure
• open channel flow
• particle image velocimetry
• river beds
• roughness