Influence of the structure of cylindrical mobile flumes on hydraulic performance characteristics in U-shaped channels

Small U-shaped channels are widely used in irrigation districts. Accurate flow measurement in U-shaped channels is an important aspect to field water management. In open channels, mobile flumes are widely used for flow measurement because of many advantages such as low cost, no sedimentation and moveable. However, how the structure of the flume influences hydraulic performance is still unclear. The principles for designing or optimizing mobile flumes are also lacking. In this study, FLOW-3D software was used to numerically simulate the flow pattern of three cylindrical mobile flumes that are most often used in U-shaped channels, including circular cylinder, elliptical cylinder and V-tailed cylinder mobile flumes. The hydraulic characteristics including backwater height, energy loss and flow measurement accuracy were analyzed. The results showed that under the same working conditions, the fluctuations of the stagnation point depth in the elliptical flume were the smallest. The backwater height and the energy loss in the V-tailed flume were the lowest. The contraction section of the cylinder could be designed as a curve with large curvature to make the upstream water flow more stable. The diffusion section could be designed as V-tail to improve flow pattern and reduce energy loss. Under a safe backwater height, the throat length could be increased to improve the submergence degree.