| Irrigation district is a large agricultural water user in China.With the continuous expansion of field irrigation scale in China,to develop water-saving agriculture,to improve irrigation water utilization,and to enhance the irrigation water management have become the only way which must be passed for sustainable agricultural development.Due to its advantages of good hydraulic conditions,good anti-seepage effect,strong resistance to external forces and space-saving,U-shaped channels have been widely used in major irrigation areas in China since the 1970s.Although the U-shaped channel has been widely used,its current measuring technology is not perfect.The current measuring device cannot meet the requirements of high precision and practicality of U-shaped channel,so it is necessary to find a convenient and fast method and precise measurement of flow measurement devices is necessary,besides systematic study of the U-channel flow velocity distribution and hydraulic characteristics,are also urgent need to solve the application of theoretical problems in irrigation area.Based on this,this paper proposes a new type of U-channel flow measurement device—D50U shaped channel-column composite flow measurement device,which conducts experimental research under the uniform flow conditions for the D50U shaped channel.The measuring device tests the flow velocity and water level of the cross section,analyzes and finds the regularity to investigate the flow measurement method of the open channel flow.The following main conclusions are obtained through research:1.In the process of measuring the flow by the composite plate-column flow measurement device measures,the angle of deflection of the angle plate increases with the increase of the flow rate in the channel.This paper concludes the relationship between the angling plate deflection angle and the flow rate of the channel flow in the process is a linear function,and the measurement flow is calculated asQ=m?sin??52.2.Fit the relationship between the deflection angle of angle plate,channel slope and channel flow in the process of measuring the flow of plate-column composite flow measurement device.The fitting relationship is:Q=1185sin25×i0.05234+2.021.3.In the process of measuring flow of the plate-column composite flow measurement device,the water level increases with the increase of the water flow.This paper concludes that the relationship of the water level and flow in the channel is a quadratic polynomial function relationship.4.Under the same control flow,the change of channel surface elevation is positively correlated with the slope of channel slope;under the same gradient,the change of channel surface elevation is positively correlated with the flow through channel.5.According to the statistical analysis of the contour maps of actual flow velocity measured on the D50U shaped channel,it is concluded that the flow velocity at the mid-perpendicular line is the largest and it decreases toward both sides of the channel side wall;the maximum flow velocity position is located at the vertical line of the cross-section,and this position is not affected by the gradient of the channel slope;the velocity of the flow in the same layer is the minimum at the side wall.6.According to the statistical analysis of the maximum flow velocity,the maximum velocity of the vertical line in the cross-section of water is basically located at the water depth of 0.5-0.9 times.7.Comparing the calculated values of the different lateral flow velocity distribution formulas with experimental measured data for the D50U shaped channel,the parabola-type function was used to fit the lateral flow velocity distribution.The correlation coefficient was above 0.9 and the maximum relative error was 3.8%.From this,it can be concluded that the distribution of the lateral flow velocity in the D50U shaped channel plate-column composite flow measurement device conforms to the parabolic function.8.This paper analyzes the applicability of logarithmic function relations,parabolic function relations,and dual power law type functional relationships in describing the distribution law of vertical velocity.Through comparison,it is found that the parabolic function relation is more suitable to describe the flow velocity distribution,and the maximum relative error is 2.04%,it was concluded that the distribution of vertical flow velocity in the D50U channel-column composite flow measurement device conforms to the parabolic function.The test results in this paper can provide a theoretical basis for the promotion and application of U-shaped channel flow measurement for plate-column composite flow measurement devices. |
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