Study On Hydraulic Performance Of Triangle Long-throated Flume For Furrow Irrigation

Water measurement in irrigation area is an important prerequisite and foundation for scientific water allocation,water saving and quota management in irrigation area.It becomes more and more important for popularization and implementation of water measurement technology.When the amount and time of irrigation in the field are accurately matched with the water requirement of the crop,the goal of efficient water-saving production can be achieved.A great deal of scientific research work has been done on crop water demand and abundant achievements have been achieved.But at present,the research of water measurement technology is mostly directed at the specification channel,which is difficult to apply to the field ground conditions and flow range,to achieve small flow measurement into irrigation ditches,and to accurately judge the relationship between crop water demand and actual irrigation water consumption.Therefore,aiming at furrow irrigation,which is the most widely used field irrigation method in northern China,it is particularly important to propose a new type of water measuring equipment with strong applicability and low cost to meet its water demand.The outline of the simple Long-throat measuring flume for furrow irrigation proposed in this study is a trapezoidal section close to the form of irrigation ditch,and the throat section is triangular,which is suitable for precise measuring water under small flow rates of furrow irrigation.The hydraulic characteristics of flume under different operating conditions and different structural parameters were investigated by means of experiments and numerical simulation.The main research contents and conclusions are as follows:(1)Based on the research of the existing measuring flume,combined with the form size and flow range of furrow irrigation ditch in northern irrigation area,two triangular long-throated flume with different shape parameters were designed for different operating conditions.According to the principle of critical flow and energy conservation,the flow formula of flume for furrow irrigation is derived.(2)The prototype experiments of triangular long-throated flume was carried out on the bottom slope of 1/10000.The variation of surface line,Froude number and specific energy of cross section under different discharge and outflow conditions was analyzed.Then the specific position of the critical water depth section in the throat section is determined,to get the optimal value of the throat length.Also,the flow formulas under free and submerged outflows are fitted,with average and maximum errors bing within 5% when the calculated discharges are compared with the actual ones.In addition,the critical submergence values of flumes 1 and 2 are stably distributed between 0.80 and 0.86,which change slightly with flow rate.(3)Flow-3D based computational fluid dynamics(CFD)method is used to simulate the internal flow movement of triangle long-throat flume.The maximum relative error between the experimental water depth and the simulation value is less than 10%,variation law of two water surface lines coincides with each other,indicating that the simulation results have higher precision.Based on the advantages of numerical simulation,the internal flow field of flume is deeply analyzed,and the distribution law of longitudinal and transverse time-average flow velocity and turbulence intensity is obtained.(4)Based on prototype test with five kinds of bottom slopes in the range of 1/500~1/10000,we explore the influence of different bottom slopes on the hydraulic characteristics of flume.The water surface lines in the measuring flume under different bottom slopes are generally close,and the change of bottom slopes has little effect on the water depth in throat control section.Fitting the relationship between water depth and discharge at section 5 under all bottom slope conditions,a general flow measurement formula is obtained in the range of 1/500~1/10000 bottom slope,and the formula has high accuracy.The flow range and ground conditions applicable of each flume are obtained,and the influence of the bottom slope change on the water surface line and the longitudinal flow velocity is analyzed.The optimized value of the throat section length is obtained for each flume by calculating the position of the critical water depth.