Lateral Variation of Turbulent Features in Developing and Developed Narrow Open-Channel Flow

Abstract

In the present study, a detailed experimental investigation of lateral variation of turbulent characteristics is carried out in developing and fully developed flow over a fixed rough bed. Experiments are conducted in a rectangular flume of aspect ratio $(b/h = 3.05)$ and bed roughness $d_{50} = 2.5\,{\text{mm}}$. Instantaneous three-dimensional velocities were measured using a Nortek Vectrino plus downlooking ADV. The characteristics of normalized flow velocity, turbulent intensities, Reynolds shear stresses and TKE distribution have been investigated. Raw velocity data have been filtered as prescribed in the recent literature. From the experimental data, it is observed that boundary-layer thickness increases along the streamwise distance in the developing flow region and reaches maximum in fully developed flow. On the contrary, boundary-layer thickness decreases in the lateral direction from the centreline of the channel towards sidewalls in both developing flow and fully developed flow. Local shear velocities are estimated from the Reynolds shear stress distribution in intermediate layer. Lateral variation of shear velocity shows decreasing trend in both developing and fully developed flow from the centreline towards sidewalls. Velocity dip phenomenon due to secondary current is observed in both the vertical distribution of normalized streamwise velocity profiles and RSS distribution along the lateral direction near to the side wall in both the developing flow and fully developed flow. Normalized Reynolds shear stress decreases in the lateral direction from the centreline of the channel towards the side wall in the developing flow with retardation of flow in the outer layer.