Investigating the hydrodynamic characteristics of the multiple rectangular Lopac gates in submerged flow

Background and Objective:Today, due to the reduction of water resources and the issue of excessive water consumption in the agricultural sector, for the purpose of distribution, delivery, and flow regulation to waterways, and to prevent water losses, novel structures with better efficiency and easier operation have been introduced by researchers. Lopac gates are one of the hydraulic structures for flow control and regulation, which have features such as the possibility of automation, open-channel flow, and easier installation and placement compared to other structures. In this study, a rectangular multi-lopac gate, which is one of the novel types of lopac gates, has been used. Considering the easier operation of smaller gates compared to larger gates, in this study, has been investigated the effect of two smaller gates instead of a single gate on the hydraulic characteristics in the submerged condition with 70%, 80%, and 90% submergence levels and with the aim of increasing efficiency and ease in design and construction.Materials and Methods: In the present study, several simulations were performed to validate and select the turbulence model. After investigation the performed simulations, a mesh of 800,000 cells, the RNG turbulence model, and a time of 40(s) for the flow to reach stability were selected.Then, to investigate the hydraulic parameters of maximum shear stress, maximum force acting on the gate, velocity distribution range, and shear stress in the rectangular lopac gate under submerged flow conditions, and compare it with the single gate case, simulations were performed at three discharges of 25, 35, and 45 (l/s), opening angles of 35, 40, and 45 degrees, and submergence levels of 70%, 80%, and 90% in two different geometries, with a total of 54 simulations.Findings: The results showed that the maximum shear stress has an inverse relationship with submergence and opening angle, and the maximum horizontal force acting on the gate has a direct relationship with submergence and discharge. It was observed that all the investigated parameters in the two-gate case decreased compared to the single-gate case, and the amount of this decrease in the horizontal force acting on the gate was 33.5%, which was the highest decrease at a discharge of 25(l/s) an opening angle of 45 degrees, and 90% submergence, and the lowest decrease was at a discharge of 25(l/s), an opening angle of 45 degrees, and70% submergence. The reduction in the maximum shear stress in the two-gate case compared to the single-gate case was 13.25%, with the highest decrease of 23.29% occurring at a discharge of 45 (l/s), an opening angle of 45 degrees, and 90% submergence, and the lowest decrease of 6.21% occurring at a discharge of 45 (l/s), an opening angle of35 degrees, and 80% submergence.It was also observed that the distribution range and elongation of velocity and shear stress on the flume bed increased with increasing discharge and opening angle, and in general, the distribution range and elongation of velocity and shear stress on the flume bed decreased in the two-gate case compared to the single-gate case.Conclusion:According to the results, it can be stated that the distribution range of velocity and shear stress has a direct relationship with discharge and opening angle, and the elongation of the velocity and shear stress distribution in the two-gate case decreased compared to the single-gate case.The maximum shear stress has an inverse relationship with the opening angle and submergence, and it decreases by 13.26% compared to the single-gate case.Investigating the maximum force acting on the gate showed that this parameter has a direct relationship with flow rate, opening angle, and submergence, and it decreases by33.5% in the multi-gate cases compared to the single-gate case.