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梯形渠道测控一体农闸水力性能数值模拟及试验研究

Numerical simulation and experimental study on the hydraulic performance of trapezoidal channel measurement and control integrated agricultural sluice

  • 摘要: 为提高灌区末级渠系流量测控精度,针对梯形渠道分水口,该研究设计了一种测控一体农闸,系统探究该农闸的水力性能及影响因素。通过物理模型试验与数值模拟,分析农闸不同来流量Q0、农闸开度e1及节制闸开度e2对应过闸流量Q1时的闸前后水面线、佛汝德数Fr、分流比R和流量系数μ1的变化规律。结果表明:农闸闸前水面波动幅度随开度的减小而减小、佛汝德数Fr小于0.5,闸后产生水跃,流态整体平稳可控;分流比R与相对开度e1/H呈线性关系,过流能力随堰高P的增大而降低;3种糙率n、底坡i和边坡系数m条件下μ1与e1/H均呈幂函数关系,R2大于0.97。基于因次分析法,构建流量计算式,并在自由出流和淹没出流2种流态下对其精度进行验证,结果显示R2均大于0.94,误差绝对值小于5%的数据比例大于87%,测流公式满足灌区量水设施精度要求,可用于梯形渠道农闸流量测量计算。研究可为灌区渠道闸门体型设计及设备应用提供参考。

     

    Abstract: Precise flow measurement and control is often required in the terminal canal networks of irrigation districts. This study aims to examine the hydraulic performance of integrated measurement and control agricultural sluice gate at the trapezoidal channel diversion outlet. Geometric and field frameworks were also established for such sluices. Experimental measurements and numerical simulations were conducted to determine the influencing factors on the water surface profile upstream and downstream of the regulating sluice, the variation of Froude number Fr, the diversion ratio R, and the discharge coefficient μ1 of the agricultural diversion sluice under different sluice openings e1 and e2. Steady-state flow was modeled using volume of fluid (VOF). Four grid resolutions were evaluated for grid independence verification. The governing equations included the transport, continuity, Reynolds-averaged, turbulent kinetic energy and dissipation rate equations. The equation system was discretized by the finite volume method, according to the segregated implicit iterative approach. The channel dimensions and boundary were matched with the experimental setup. Four evaluation metrics were selected to verify the simulation accuracy: the maximum absolute relative error (MARE), mean absolute percentage error (MAPE), coefficient of determination (R2), and root mean square error (RMSE). Dimensional analysis with dimensional homogeneity was employed to derive the overflow formula for agricultural sluices. Grid independence analysis demonstrated that the grid was refined to 1.5 cm or finer, indicating the negligible variation in water depth at the monitoring point. Grid quality exceeded 0.8 for all four resolutions, indicating the accurate grid generation and reliable simulation. Experimental data were validated by the maximum absolute relative errors of 9.96% and 7.08%, respectively, for flow rate through the sluice and water depth h1 in front of sluice. The mean absolute percentage errors were 3.91% and 1.64%, respectively. Coefficients of determination reached 0.986 and 0.985, respectively. Root mean square errors were 1.14 and 0.45, respectively. Water surface fluctuation upstream of the agricultural sluice gate decreased, as the sluice opening was reduced. The upstream Froude number remained below 0.5 under all hydraulic conditions. The opening of the regulating sluice lowered the upstream water level, thereby weakening the backwater effect induced by the agricultural sluice. An unstable hydraulic jump formed downstream. Both the height and longitudinal extent of the jump diminished, as the regulating sluice opening increased. The flow regime remained stable and controllable in the tested range. A positive linear relationship was observed between the relative opening e1/H and the diversion ratio R under different inflow rates Q0, which remained valid when varying the side slope coefficient m and sluice width b1. The weir height P reduced the flow capacity of the lateral channel, leading to a decrease in the diversion ratio R. The discharge coefficient of the agricultural diversion sluice and the relative opening e1/H exhibited a power-function relationship under different channel parameters, with R2 > 0.97 and a mean relative error below 5%. Nonlinear regression was applied to fit discharge prediction formulas for both free- and submerged-flow conditions, with R2 > 0.94. The proportion of predictions within ±5% of measured values exceeded 87%, indicating high prediction accuracy. Mean relative errors were consistently below 5%, fully meeting the technical standards for flow measurement facilities in irrigation canals. Field test was conducted to verify the gate discharge capacity in the terminal canals of the irrigation districts. Prediction errors remained within 5%. The diversion sluice has strong applicability, low cost, and ease of promotion, which reduces operational difficulties in practical irrigation. The arrangement of agricultural sluice along the channel wall provides a reference for developing the intelligent integrated measurement and control sluice equipment. The findings can also provide a strong reference to design channel sluice shapes and equipment applications in irrigation areas.

     

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