فهرست نشریات علمی دسترسی آزاد ایران

This study aimed to evaluate the hydraulic performance of a semi-circular rotary gate in a rectangular canal, focusing on the effects of gate opening angles and gradually transition lengths on flow behavior, including discharge and discharge coefficient. To accommodate the gate, the canal cross-section gradually shifted from rectangular to semi-circular over three transition lengths: 0.6, 0.9, and 1.2 m. Laboratory experiments were conducted under varying flow rates, upstream water depths, and gate openings in free-flow conditions. The discharge coefficient increased with larger gate openings but decreased as transition length increased. Two discharge estimation equations were developed, with the dimensional analysis approach providing more accurate predictions than the conventional stage–discharge method. Ignoring transition length in simplified calculations led to significant errors. The discharge coefficient varied with gate opening angle: 0.18–1.35 for 0.6 m, 0.17–1.29 for 0.9 m, and 0.15–1.23 for 1.2 m transitions. The proposed equations reliably predicted discharge, with experimental and computational results showing a mean error below 5%. These findings highlight the critical role of including transition length in design calculations for accurate performance assessment of semi-circular rotary gates in irrigation systems.