Hydraulic characteristics and flow regulation model of open channel based on the joint regulation of gate and weir

Open channel water conservancy control components, especially gates and weirs, are widely used in most Chinese irrigation areas. They are important tools for water distribution and flow regulation, and play a crucial multifaceted role in improving the efficiency and effectiveness of agricultural irrigation systems and optimizing water resource management. In response to the inaccurate flow regulation of downstream flow in open channel irrigation in the arid areas of the northwest, resulting in low water resource utilization and crop yield loss, this paper proposes to control downstream flow through joint regulation of gates and weirs. First, through theoretical analysis of the hydraulic characteristics and flow formulas of gates and weirs in open channels, combined with FLUENT fluid simulation and single-factor experiments, it is found that the key parameters affecting the flow rate of open channels under joint gate - weir regulation are water level before gates, flow velocity before gates, and water level before weirs. The water level before gates, flow velocity before gates and gate opening are positively correlated with downstream flow, while the water level before weirs is negatively correlated with downstream flow. In terms of simulation model construction, a three-dimensional model of open channels, gates and weirs was established using SolidWorks. In FLUENT fluid simulation software, the simulation model is established using the SST k-ω turbulence model and the VOF multiphase flow model. In order to explore the interaction between factors and build a precise flow regulation model, the water level before gate, velocity before gate, water level before gate, and the water level before weir were selected as the test factors, and the flow rate in the downstream is used as the evaluation indicators, and the box-behnken design (BBD) response surface test of the four factors and three levels was carried out. After 29 simulations under different parameters, the simulation test results show that the increase of gate opening and water level before gate under the control of gate weirs, the decrease of the flow velocity before gate and water level before weir makes the downstream flow velocity and liquid level more stable and the flow rate is more stable. The results of the variance analysis show that the water level before gate, velocity before gate, gate opening, water level before weir have a significant impact on flow rate; the correlation coefficient R²=0.9905 established open channel flow regulation model has good prediction accuracy. The response surface analysis shows that the water level before gate, flow velocity before gate, and water level before weir have a significant impact on the flow rate. Specifically, the interaction terms between the water level before gate and the gate opening, as well as the water level before weir and gate opening, will also have a significant impact on the flow rate. Finally, through the automated transformation of the existing manual gates, a field test platform for open channel flow regulation was built to realize automatic gate control, reducing the experimental error of manual operations. The field test results show that under the joint adjustment of the gate and weir, the relative error between the model predicted flow and the actual flow is less than 12%. The finding can provide ideas for the regulation of open canal flow in irrigation areas.