Laboratory study of the application of semicircular rotary gates in rectangular canals under submerged flow conditions

This study investigates the hydraulic performance of semicircular rotary gates in rectangular canals under submerged conditions, addressing the need for accurate flow measurement. Rotary gates, similar to sluice gates, regulate water level and flow. The research experimentally examines the gates’ hydraulics and the gradual transition from rectangular to semicircular cross sections of varying lengths. Laboratory flume tests were conducted with three transition lengths, five submergence ratios, and gate opening angles from 35 to 85°, across discharge rates of 0.020–0.038 m3/s, focusing on the effects on discharge, modular limits, and energy losses. The results showed that the increased gate angle increases discharge coefficient but the increased transition length decreases it. Also, the discharge reduction factor decreases with the increasing submergence ratio. Equations were developed to predict the discharge coefficient and rotary gate discharge reduction under the submerged flow, showing good agreement with experimental data. In addition, the results indicate that the transition length has no significant effect on energy loss in submerged-flow conditions. The energy loss of the rotary gate under these conditions is a function of the gate’s opening angle and the submergence ratio. Finally, an equation to calculate energy loss under submerged flow was provided.