Inclined Open Channels: The Influence of Bed in Turbulent Characteristics of the Flow

Abstract

In this paper the characteristics of turbulent flow in an open inclined channel are studied experimentally for impermeable and permeable bed. For the simulation of porous bed two different types of permeable bed with the same thickness $\mathrm {h_{v}=2\,cm}$ and the same porosity $\upvarepsilon =0.80$ are used: (a) flexible vegetation with grass and (b) gravel bed. Laboratory experiments were used for the calculation of turbulent velocity profiles. The measurements were obtained using a two-dimensional (2D) Particle Image Velocimetry (PIV). The experiments were conducted in the laboratory of Hydraulics in the department of Civil Infrastructure Engineering of Alexander Technological Educational Institute of Thessaloniki, Greece. The measurements were conducted at a $12 \times 10\,\text {cm}^{2}$ region in a distance of 4 m from the channel’s entrance, where the flow is considered fully developed. The total discharge was estimated using a calibrated venture apparatus. Measurements of velocity were taken for inclined channel for four different slopes $(\mathrm{S}\,=\,2, 4, 6\,\text {and}\,8\,\permille )$ and for three different total heights (h $=$ 5, 10 and 15 cm). The experiments were conducted for (a) impermeable bed and (b) permeable bed. Results showed that the presence of porous bed in inclined open channels influence significantly the turbulent characteristics of the flow such as the variation of longitudinal turbulent intensity $\mathrm {u'/U}_{*}$, the variation of vertical turbulent intensity $\mathrm {v'/U}_{*}$ and the turbulent kinetic energy. The channel slope doesn’t influence the Reynolds stress. Also, the type of porous bed influences with different way the turbulent characteristics of the flow.