Study on the hydraulics of vertical trapezoidal sluice gate under free flow conditions

Vertical trapezoidal gate is a new type of flat gate, which has advantages over conventional rectangular gates in flow control and diversion applications in irrigation areas at all levels of trapezoidal channels because it does not need to build auxiliary buildings such as gate chambers and torsion surfaces and occupies a smaller area. The overflow boundary conditions of trapezoidal gates are different from those of rectangular gates, in this study, a total of 186 tests were conducted for studying the hydraulic performance of the trapezoidal-shaped sluice gates built in the trapezoidal canals with side slopes of 1.5, 1.75 and 2, respectively. The effects of parameters such as gate opening e and water depth in front of the gate H0 on the flow pattern and discharge after the gate were analyzed, and the dis¬charge calculation method for free outflow of trapezoidal gates was studied based on the test data. The results indica¬ted that the outlet flow through the gate were divided into three jets. The collision of the jets forms a hump, which results in a contracted cross-section with the smallest water surface width, the largest water depth at the centerline. When the discharge and the relative opening of the gate are doubled respectively, the distance of the hump from the gate changes from 3.6e and 8.2e to 6.0e and 3.3e, and the height of the hump changes from 1.5e and 3.0e to 2.4e and 1.5e, and the distance required for the water flow in the channel downstream of the hump to be evenly distribu¬ted changes from 15.Oe and 33.Oe to 34.Oe and 17.Oe. The flow exhibited wavy appearance with alternate contraction and expansion in streamwise and width direction due to the interchange between kinetic and potential energies, and the fluctuation decreased with the dissipation of total energy. The average relative error of the flow coefficient formu¬la obtained was 2.17% , and the data with relative errors less than 6% accounted for 96.3%. The results can provide reference for the engineering design and operation management of trapezoidal sluice gate in practice. © 2023 China Water Power Press. All rights reserved.