| Open channels are the main transportation channels for industrial wastewater,urban domestic water and agricultural irrigation.Accurate flow measurement in channel transportation has important practical significance for the sustainable use of water resources.It can not only provide scientific guidance for water distribution in irrigation areas,but also help realize the improvement of water use efficiency and the rational allocation of water resources.Therefore,the research on canal water measurement devices with durability and practicality,high measurement accuracy,small head loss,simple flow calculation formula is an irrigation water measurement technology urgently needed in modern irrigation areas.Compared with other cross-sectional shapes,rectangular channels have the advantages of less cultivated land,simple construction technology and low construction cost,and are widely used in the last level channels in irrigation areas.Therefore,research on water measuring equipment suitable for rectangular channel has important practical value for scientific water use in irrigation area.In this paper,in order to explore the hydraulic characteristics and applicable conditions of NACA airfoil flume,optimized airfoil flume,cut-throat flume,and airfoil type flume in rectangular channels,four kinds of flume in rectangular channel with different flow and shrinkage ratio were studied by test and numerical simulation.The research contents and conclusions are as follows:(1)This paper uses the VOF model to conduct three-dimensional simulation research on four flumes.Through comparative analysis with tests,the water surface line and flow pattern change laws under various working conditions are obtained.The data obtained from numerical simulation and tests are compared and found.The change rules of the two are basically consistent,indicating that the numerical simulation method is more reliable for the study of rectangular channel measuring flume.(2)According to the size of the channel,the flow range of 5-27L/s is selected for hydraulic characteristics test.This paper uses three kinds of shrinkage ratios,a total of 144 sets of test conditions.According to the test results,the flow field,Froude number,critical submergence degree,backwater height,head loss and other hydraulic characteristics of the four flumes in the rectangular channel are comprehensively and systematically analyzed.Through the flow velocity distribution along the way and the flow velocity distribution of the water cross section of the four flumes,it is found that the flow of the optimized airfoil flume is the most stable;the Froude numbers of the four flumes increase first and then decrease from upstream to downstream,reaching the maximum in the diffusion section of the flume,the Froude number of the airfoil type flume is the smallest.The water depth of the downstream channel of the flume was changed by adjusting the tailgate to obtain the upstream and downstream water depths under the critical outflow state.It is believed that the flow has little effect on the critical submergence degree,the critical submergence degree of the optimized airfoil flume is the largest;the same kind of flume,when the shrinkage ratio is the same,the height of the backwater increases with the increase of the flow rate,it decreases with the increase of the shrinkage ratio;the head loss of the same water flow tank decreases with the increase of the shrinkage ratio under the same flow,the head loss increases with the increase of the flow under the same shrinkage ratio.(3)Dimensional analysis and the principle of energy conservation are used to deduce the water level and flow relationship of NACA airfoil flume,optimized airfoil flume,cut-throat flume,and airfoil type flume in rectangular channels.The corresponding flow calculation formula is obtained by combining the relevant data,the error analysis is carried out.The results show that the formulas derived by the two methods are simple and practical,meet the requirements of measurement specifications.tests and numerical simulations of four flumes on rectangular channels show that the optimized airfoil flume has better applicability.The results show that the optimized airfoil flume has better applicability and broad application prospects in rectangular channels,which can provide a certain theoretical reference for the in-depth study of water measurement in irrigation areas. |
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