Experimental And Numerical Simulation On Hydraulic Characteristics Of U-Shaped Channel Triangular Profile Weir

Accurate water measurement is very important for the development of water-saving agriculture.It can not only provide a scientific basis for water distribution in irrigation areas,but also realize the purpose of efficient utilization of water resources,improve the scientific management level of irrigation areas.U-shaped channel is a common form of the last channel in irrigation area,which has strongly resistant to freezing,superior hydraulic performance and is not easy to be silted.Therefore,the study of water measuring equipment with simple structure,low cost and small head loss has important practical value for scientific water use and water conservation in irrigation area.In this paper,a three-dimensional model of U-shaped channel triangular weir is established by Auto CAD and meshed in Gambit.Based on computational fluid dynamics simulation software Fluent 6.3,RNG k-? turbulence model and VOF method are used to simulate the triangular weir under different conditions.Some of the main research contents and conclusions are as follows:(1)Based on the structure and flow measurement principle of triangular section weir,field tests of triangular section weir with U-shaped channel are carried out under different weir height.The numerical simulation of water level,velocity and discharge were compared with experimental,and the variation law of water level and velocity obtained by the two methods is obtained.Similarly,the maximum relative,error of calculation is 4.39%.This shows that the numerical simulation method is more reliable for flow measurement research.(2)According to the simulation results under different weir height,bottom slope and slope conditions,the flow coefficient of U-shaped channel triangular weir is fitted and the flow formula is established.The flow coefficient of triangular weir under different conditions is basically stable in the range of 0.6162-0.6454,and the average value of 0.631 under different conditions is taken as the flow coefficient of U-shaped channel triangular weir.The maximum errors of H50D50,H40D30 and H80D80 channels are 3.90%,4.84% and 4.93% respectively,and the average relative errors are 1.84%,3.45% and 3.54% respectively,which accord with the requirements of flow measurement standards.(3)The flow coefficient of U-shaped channel arc-top triangular section weir is 0.637 by fitting the simulation results under different weir height,bottom slope and slope conditions,and the maximum relative error is 3.50%,4.50%,4.78%and the average relative error is 1.53%,2.22%,3.03% by comparing the calculated discharge with the simulated discharge.All meet the requirement of flow measurement in irrigation area and are smaller than standard triangular weir.(4)Under the conditions of different slopes,bottom slopes and weir heights,the variation laws of surface line,velocity field and flow pattern in upstream and downstream of triangular section weir are analyzed and explored,and the pattern of weir flow is obtained from slow flow to rapid flow and then to slow flow.The variation of head loss,critical submergence degree and backwater height of U-shaped channel triangular section weir and its influencing factors were studied under different conditions.Weir height has the greatest influence on head loss and the maximum head loss of standard triangular section weir is 0.057 m.The main influencing factors of backwater height are weir height,which increases with the increase of weir height,decreases with the increase of bottom slope,and increases with the increase of slope.The critical submergence degree is directly proportional to weir height,bottom slope and flow rate,and inversely proportional to slope coefficient,and the range of variation is 0.76-0.96.The maximum head loss of arc top triangular section weir is 0.035 m,the critical submergence is between 0.87-0.97,and the backwater height is 0.08 m.Comparing the hydraulic characteristics of arc top triangular section weir with standard triangular section weir,it is found that the hydraulic characteristics of arc top triangular section weir are better.In the course of the research,the field validation of the numerical model is carried out only in the channel with the same parameters,and only based on free outflow.The performance and application of the triangular weir with different sizes of channels and submerged flows need further study.