| Water measurement technology in farmland irrigation area is a basic technology for the development of water-saving agriculture in China,and it is also one of the basic technologies to solve the uneven distribution of water consumption in time and space.Combining the characteristics of irrigation water in farmland irrigation districts in northern my country,researching new water measuring equipment that is more suitable for irrigation districts with higher sand content in irrigation water in northern my country is of great significance to the management and development of irrigation districts.The wing-shaped water measuring flume is a new type of water measuring equipment obtained by optimizing and simplifying the original airfoil-shaped water measuring flume based on the aerodynamic Hicks-Henne equation.The simplification and optimization did not change the characteristics of the original organic airfoil measuring flume for smooth flow and high flow measurement accuracy,and simplified the original complex polynomial equations to the combination of ellipse equations and tangent arc equations.In this research,through the method of combining the production and experiment of 1:1 hydraulic model with FLOW-3D software,the feasibility study and the theoretical derivation of the flow measurement formula of the imitating wing-shaped measuring flume in different prismatic channels were carried out.The main research results obtained are as follows:(1)In this study,10m×60cm×30cm rectangle channel in the lateral contraction type imitation wing shape flume experiment,and the FLOW-3D numerical simulation software has increased more groups of model,validated the simulation accuracy,the analysis of the hydraulic performance: upstream Froude number is less than 0.5,the critical flow near throat,downstream restore flow state;The local energy loss of water flow in each section is obtained from the head loss analysis,so as to better understand the overall movement of water flow;Influence of flow rate,shrinkage ratio and wing length on water surface line.A total of 528 sets of data were obtained from the experiment and numerical simulation.According to Buckingham theorem and the assumption of incomplete self-similarity,the flow measurement formula of double circular arc flume was derived,and the error of the formula was less than5%.(2)The wing-shaped groove was merged and placed in the center of a rectangular water flume of 17m×70cm×100cm to obtain a portable wing-shaped water measuring device,and FLOW-3D software was used to supplement several groups of models for numerical simulation.After verifying the accuracy of the simulation,the hydraulic performance of the wing imitating water measuring device is analysed.The Froude value at the upstream crosssection measurement point meets the water measurement standard of China’s irrigation district,and the critical flow occurs near the throat,and the downstream regress to the slow flow state.A total of 84 sets of data were obtained from the experiment and numerical simulation.According to Buckingham theorem and the assumption of incomplete self-similarity,the flow measurement formula of the impersonating wing flume was obtained,and the average error of the formula was 6.34%.The backwater height is 3.25 cm in average and 6.32 cm in maximum.(3)The portable water measuring device is placed in the trapezoidal channel with the same flow area in the rectangular channel,so as to compare the flow measuring effect with that in the rectangular channel.A total of 35 groups of data were obtained from the test,and the hydraulic characteristic parameters were analyzed: when the flow exceeded 25L/s,the Froude number of the upstream would be higher than 0.5,which could not meet the standard of flow measurement in the irrigated area and would cause a large error in flow measurement.The height of backwater increases with the increase of the flow rate and decreases with the increase of the shrinkage ratio.The maximum backwater height is 9cm,the flow is 40L/s,and the shrinkage ratio is measured under the condition of 0.50.The minimum backwater height is4.06 cm,the flow is 10L/s,and the shrinkage ratio is measured under the condition of 0.66.The average backwater height is 7.04 cm.The average value of head loss was 16%,the maximum value was 22.6%,and the minimum value was 11.1%.The water head loss range is mainly distributed in the range of 13%～18%.Combined with hydraulic model test and numerical simulation,the feasibility analysis of portable airfoil flume in rectangular channel and trapezoidal channel is carried out.By analyzing the range of the optional shrinkage ratio and the flow range that can be accurately measured in different channels,the applicability range of the optimized aerofoil flume is obtained. |
PDF Full Text Request