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

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.