Study On Flow Characteristics Of Automatic Metering Plate Gate Of Open Channel Based On CFD

In our country, agricultural water use efficiency is less than half of that in the developed countries. Measured irrigation is the trend of the agricultural irrigation in our country. Its linchpin is to develop the plate gate system with measured function. Water level, velocity and pressure are the main factors which affect the accuracy of the measurement. Research on the distribution and variation of water level, velocity, pressure behind and in front of the plate gate in open channel, contribute to select the mounting location of the sensors and improve the structure of the open channel. Thereby, it contributes to improve the accuracy of the sensors with important theoretical significance.For two mounting methods of the gate:angle iron frame and slot aluminum frame, Fluent is used to simulate the flow of the plate gate in the open channel.When the gate is mounted by angle iron frame method, according to the different flow and opening condition,35cases are designed. Pressure-based solver is used to solve the discrete governing equations, standard k-ε is used to process the turbulence problem, VOF model is used to process the free surface problem. The results show that the steady range of the flow field is1.5m-2m and6.4m-7m. It is easier to get steady flow when the opening is0.3m,0.4m,0.5m. When the initial water level is higher than0.8m, the opening should avoid being less than0.3m, for which can get fully outflow to ensure the safe operation. To reduce the velocity of the downstream and improve the stability of the flow field, structure of the open channel is improved:the length of the contraction section is shortened to1.01m.9cases with poor stability of flow field are selected to be verified by simulation. Its flow field is steadier than other cases. The flow velocity is reduced by0.6m/s-0.8m/s, and the stable range of the flow field is increased by1m-1.5m. This is conducive to accurate measurement of the sensors. And, the rationality and effectiveness of the improvement are proved.When the gate is mounted by slot aluminum frame method, some cases with stable flow of the angle iron frame method,6cases are designed. Because of the cancelling of the lug, the downstream velocity is faster than other cases. Its velocity is0.8m/s higher than it of angle iron frame method. To decrease the velocity, a stilling basin is built0.346m behind the gate, which size is1.8m of the length and1.2m of the width. Compare with no stilling basin, the velocity of the flow field behind the stilling basin decreases by0.6m/s-1.4m/s, the flow reaches a more stable condition in the range of0.4m-2.2m and6m-7m, and the velocity distribution on vertical section is uniform. It’s suitable to mount the sensors.The simulation results of the two mounting methods have important reference value for the promotion and rational use of the automatic metering plate gate.