Study On The Hydraulic Characteristics And Influence Factors Of Measuring Plate In Small Canal

Irrigation area water measurement technology is the basic means to realize the optimal allocation of water resources and modern agricultural water management.The terrain in the northern irrigation areas of China is gentle,the sediment content of the irrigation flow is large,and the existing water measuring facilities are prone to sedimentation.Therefore,it is important to study new water measuring facilities that are not clogged and have high flow measurement accuracy,which is an important application for improving the modern management level of the irrigation area value.An overhanging plate that can rotate around the axis is a new type of water measuring facility designed based on the principle of conservation of momentum.It has the characteristics of a stable relationship between the deflection angle of plates and the flow rate,smooth flow of sediment during flow measurement,no siltation,and simple structure.The water measuring facility is suitable for channel flow with gentle terrain and large sediment content.In this study,through theoretical analysis,prototype test and numerical simulation,the flow measurement principle and flow calculation model of the new level horizontal plate were systematically studied.The main research contents and conclusions are as follows:(1)Based on the theory of flow around the plate,a flow calculation model based on the moment balance and momentum conservation is proposed.The lifting force on the plate is regarded as the vertical component of hydrostatic pressure,and two kinds of pressure body assumptions are proposed.According to the similarity between the flow pattern behind the plate and the flow pattern under the completely submerged outflow,a flow calculation model based on the outflow theory of gate hole is proposed.(2)According to the design of measuring flume and irrigation area channel,in order to make the flow pattern more stable when the water flows around the flat plate,the measuring horizontal plates of different shapes are designed;the physical prototype test is carried out on the U-shaped channel and rectangular channel,and the law of water surface line and Froude number along the different shapes of flat plate with different flow,bottom slope and submergence degree is analyzed.Based on FLOW-3D software,the flow of water measured by horizontal plate is simulated.Except for some working conditions,the maximum relative error of test water depth value and simulation value is less than 10%,the average relative error of deflection angle is 4.45%,and the change rule of water surface profile is the same.By means of numerical simulation,the law of turbulent kinetic energy and time average velocity along the path is obtained.(3)The influence of bottom slope and plate type on the relative head loss is analyzed.For U-shaped non full section plate,when the bottom slope and plate type are the same,the relative head loss decreases with the increase of flow.Except for the contraction ratio of 0.715,the plate is at a small flow rate(this test is about 10 L / s)when measuring the flow,the head loss ratio is more than 10%,while when measuring the flow of other plates,the head loss ratio is less than 10%,in which the maximum head loss of the contraction ratio is 0.439 and 0.337 plates is not more than 6% of the total head of the upstream;when the flow is the same,the relative head loss increases with the increase of the bottom slope when the bottom slope is 0.0005-0.001;when the bottom slope is 0.0002-0.0005,the relative head loss has little difference.(4)According to the established flow model of measuring horizontal plate,two kinds of pressure body hypothesis are verified by using the test results of rectangular channel and Ushaped channel full section measuring horizontal plate.Hypothesis 1 and hypothesis 2 are applicable to U-shaped channel,and the relative error is less than 6% when the flow is greater than 17 L / s;hypothesis 1 is applicable to rectangular channel,and the relative error is less than 10% under most working conditions,and hypothesis 2 is not applicable ? In conclusion,hypothesis 1 is more applicable.Based on the established discharge model of horizontal plate gate,the semi empirical discharge formula is obtained by fitting the test results.For the rectangular full section,the maximum error between the calculated flow and the measured flow is not more than 18%,and the calculation error under most working conditions is less than 10%.For the U-shaped plate with different shrinkage ratio,a unified flow formula is obtained.The maximum relative error between the calculated value and the measured value is 6.5%,and the average relative error is 2.6%,which meets the water demand of irrigation area.The formula is applicable to the range of bottom slope 0.0002 ? 0.001.In practical application,it is suggested to select the theoretical calculation model of gate outlet flow to measure the current,and select the horizontal plate with the contraction ratio of 0.547-0.439 u to measure the current.