Study On Hydraulic Performance Of Inclined(Flat Top) Measuring Weir In U-Shaped Channel

Irrigation water measurement is the basis for the rational allocation of water resources,it's an important means to promote the development of water-saving agriculture.It has important significance for agricultural water conservation and alleviate the shortage of water resources with high precision and strong adaptability.The developed irrigation facilities have a wide range of water measurement facilities,but they are mainly applicable to gentle slope channels with a slope of less than 1/2000.Large slopes of irrigation channels in Hexi Corridor,Gansu,most of the local small-scale channels are U-shaped sections,and the general slope is1/150-1/200.At present,there is very little research on the U-shaped channel water-flow facilities with large slopes.Based on the characteristics of U-shaped channel section,this paper designs 9 types of oblique screech sluice and 4 different sloping hull flat top sluice for the measurement of flow when the channel bottom slope is large.The over current test was carried out in the flow range of 10~40L/s,and numerical simulation was performed by FLOW-3D software.This paper analyzes the effects of changes in the water surface,the height of the water surface,the slope of the water volume on the height of the upstream drowning water,the distribution of the flow velocity,and the change in the number of floods in the Buddhist shrine.This paper also studies the relationship between water depth and flow rate at each section and draws a high-precision flow measurement formula.The specific research content and conclusions are as follows:(1)The principle of flow measurement in the U-shaped canal was studied for oblique sill(flat-top)water sluice.The flow calculation formula was obtained by combining the experimental data with the quantitative analysis principle.(2)In this paper,the free-flow test of 9 different types of oblique sill sampans under 8different flow conditions is carried out.The analysis of different sloping kerfs of different body parameters,the change of water line during turbulent flow,the height of sloping water and the upstream Buddha The changes of hydraulic properties such as Jude number.When the height of the upstream dredging does not exceed 10 cm,the suitable shrinkage ratio for the oblique screech is 0.867-0.951.The formula for measuring currents obtained by fitting the sections with the most stable water depth-flow relationship is that the relative error is within± 7%,which meets the accuracy requirements of the measurement facilities of irrigation areas.(3)This paper analyzes the free flow outflow tests of four different types of inclined scaly top pebbles on four different slope channels and seven different flow conditions.It is found that the optimization of the flow pattern is achieved.The changes of hydraulic properties,such as changes in surface line,height of drowning,and number of Falco deer,etc.,at different slopes of different channels were analyzed.In order to ensure that the height of the upstream dredging and the accuracy of the flow measurement are guaranteed at the same time,it is appropriate that the height of the slanted kerb is not greater than 12 cm.Using the principle of harmonization and combining SPSS software to establish the flow measurement formula,the relative error reaches a maximum of-4.42%,which meets the irrigation area water demand.(4)In this study,Flow-3D software was used to perform three-dimensional simulation calculations on oblique sill(flat top)sluice,and compared with the results of physical model tests.The relative error between the water surface line and the test results was within 10%,the results of the numerical simulation of the U-shaped canal(flat-top)water sluice can be used as a reference.Based on this,FLOW-3D was used to analyze the cross-sectional velocity distribution,longitudinal profile velocity distribution,and the Froude numbers in different working conditions.The distribution of flow velocity and flow field in the channel was obtained for different body masses.(5)We use the FLOW-3D software to analyze the water flow curves of the inclined planes with different lengths.It is found that when the L2>15cm,the curve of the water line changes more smoothly.With the extension of the horizontal section,the maximum value of the Froude number gradually increases,and the position of the critical water depth gradually shifts back.the changes in the number of Buddhist monks in the upper channel and the downstream channel of the quantity of waters are consistent.