Characteristics of the flow in channels with extended boundaries

Abstract

In the flow in channels with extended boundaries, the channel sides are extended covering parts of the channel flow surface symmetrically or asymmetrically. The pressure on the top surface remains approximately atmospheric, while the distributions of both velocities and discharges in the flow cross-section are severely affected. In this study, cases with different asymmetric extension ratios and aspect ratios were experimentally examined. The effect of the roughness of both extensions and the flume bed was investigated. The velocity data were sampled using Acoustic Doppler Velocimeters. The resulting velocity iso-lines showed deformations due to asymmetricity and the maximum velocity distribution was shifted towards the sides of smaller extension ratios. Low-velocity zones were formed bounded by the extensions, the side boundaries, and the flume bed where the flow resembles that of a closed conduit with maximum velocity value near the middle, but with a major difference that the iso-lines are not closed due to the absence of the fourth boundary. In cases with a larger aspect ratio and roughness, high turbulence was noticed with severe cross-currents resulting in a low-flow velocity component. Results are demonstrated through figures and tables and the data were tested against well-known equations available in the literature. HIGHLIGHTS The study examined experimentally the characteristics of flow in channels with asymmetric extended boundaries.; Eight experiments with asymmetric extensions were tested.; The Acoustic Doppler Velocimeter (ADV) was used in sampling the velocity data.; Iso-lines for flow velocity components were drawn.; The effects of aspect ratio and bed and extension roughness were discussed.;

Keywords

• acoustic doppler velocimeter
• asymmetric extension ratios
• flow in channels with extended boundaries
• rough extensions
• turbulence and cross-currents
• velocity iso-lines