عنوان مقاله [English]
Management of irrigation networks has always been one of the most important issues in the agricultural sector, and the use of modern valves and structures for controlling and adjusting the water flow is very important in irrigation channels. Water level control structures are used in irrigation canals to imple-ment delivery methods (Naghaei and Monem 2013).
Gates are one of the most used water structures in distribution canals that are used to transport and deliver water to consumer or to control the flow rate or water level. Determining the relationship governor on these structures can improve the performance of open canals and therefore prevent water loss. Lopac gate as a water level adjustment structure has recently attracted attentions and its performance in applied and practical areas of irrigation channels in different countries is accepted. The gate can be opened along the flow direction and can regulate upstream water level for various dis-charges by adjusting the gate opening angle (Oad and Kinzli 2006). So far little studies have been done on these types of gates. Some studies have examined hydraulic conditions of the flow passing through rectangular Lopac gate and presented the discharge equation as well as its coefficient in free flow and submerged conditions. In the present study, an experimental investigation has been conducted on new type of Lopac gate called elliptical lopac gates. This type of gate, which is a combination of rectangular Lopac gates and elliptical sharp edges have good function in passage of rubbish, foliage of trees and sediments along with the flow. We constructed and installed an elliptical Lopac gate as well as a rectangular Lopac gate at the laboratory scale to control and compare performance of both types of gates. The test were conducted for 5 opening degrees and for 5 discharge. Then, discharge equations of the elliptical Lopac gate in free flow condition with the help of buckingham pi theorem were presented with appropriate precision of Mean Absolute Percentage Error (MAPE = 4.44%).Also, changes in the energy flow dissipation crossing of Elliptical Lopac gate and Rectangular Lopac gate were studied and compared.