Determining the discharge coefficient in model of the triangular-rectangular combined weir and sliding gate

Introduction: Measuring flow rate in water transmission channels has always been important. weirs and gates are more useful than other measuring tools and methods due to their low cost, ease of installation, ability to regulate and control the water level, as well as relatively simple and accurate relationships. Of course, each of these structures alone has weak points; For example, the settling of sediments behind the weir and the accumulation of floating materials behind the gate reduce their efficiency. In order to eliminate or reduce the weak points of weir and gate, the combination of these two structures in different ways and the research on hydraulics and the accuracy of the flow coefficient of the combined structure have been considered by researchers for some time. Therefore, in the current research, a triangular-rectangular combined weir structure and a sliding gate were built and its flow coefficient was investigated in different hydraulic conditions by a laboratory model in the hydraulic laboratory of Birjand University.

Methodology: The experiments of this research in a laboratory flume with a length of 10 meters and a width of 0.3 meters in order to determine the discharge coefficient of the combined triangular-rectangular weir structure and the sliding gate, in two states of fixed opening of the gate and different flow rates and different opening of the gate and constant flow rates. And it was done in two slopes of 0.002 and 0.004. Finally, according to the existing relationship, the discharge coefficient of the structure was determined in different conditions. Dimensional analysis technique was used to generate dimensionless parameters and investigate the effect of these parameters on the discharge coefficient of the combined structure.

Results and discussion: The results of the experiments were analyzed after checking the correctness and refinement of the data, and the discharge coefficient of the combined structure was analyzed according to the collected data and the geometrical and hydraulic parameters of the structure. The discharge coefficient of the combined structure was calculated in constant gate openings and different discharges and different gate openings and constant discharges. Also, in order to control some of the tests performed, the discharge coefficient of the combined structure was examined in two different slopes. In all these researches, the discharge coefficient of the combined structure was between 0.6 and 0.9, and the results became more uniforme with the increase of the upstream depth (y/D). The extraction of the gate of the combined structure downstream of the structure had an effect on the numerical value of the discharge coefficient of the combined structure.

Conclusion: The test results showed that with the increase of y/D, the discharge coefficient first reaches its lowest value and then increases after the flow enters the rectangular weir and tends to 0.7. Also, by reducing the opening of the gate (H_g/D), the discharge coefficient tends to 0.7. Also, the intake of the gate of the combined structure increases the discharge coefficient of the structure. Slope changes have no effect in determining the discharge coefficient of the combined structure. The results of the current research with the results of other researchers who have worked in this field; It matches well.