Research On Hydraulic Performance Of The Primary And Subsidiary Fish Shape Measuring Flume In U-shaped Channel

Accurately measuring the amount of water used for irrigation in small channels is a crucial step in advancing the scientific management of irrigation areas,achieving fair billing for agricultural water usage,and enhancing the efficiency of agricultural irrigation.The fixed flume has poor economy,and it is easy to cause local siltation in the channel,which affects the safety of channel water delivery and the accuracy of flow measurement.While the mobile flume is relatively inexpensive to manufacture and typically does not lead to channel siltation,its structure requires further optimization to enhance flow measurement accuracy and hydraulic performance.In this study,through the application of ecological bionics and critical flow measurement theory,a fish-shaped cylinder with fish shape was proposed,and the cylinder was divided into one mother column in the middle and one sub-column on both sides to form a primary and subsidiary fish-shaped measuring flume.Using dimensional analysis,the calculation formula of flume flow suitable for different contraction ratios and different channel slopes is derived.The physical model test and computer numerical simulation(software)were used to study the hydraulic performance of the primary and subsidiary fishshaped measuring flume with different contraction ratios in the U-shaped channel,such as flow measurement and velocity distribution,Froude number in front of the flume and head loss under different channel slope and flow rate.The numerical simulation software is used to simulate the six different structures of the measuring flume.The velocity distribution,the Froude number distribution and the head loss of the six measuring flumes are studied to propose the optimization method of the measuring flume structure.The primary findings are as follows:(1)The portable primary and subsidiary fish-shaped measuring flume offers high accuracy in measuring,minimal hydraulic head loss,lower backwater height,minimal upstream turbulence,and high submergence.The average relative error of flow measurement in the flume is 1.08 %,and the relative error is 0.03 %-4.35 %.The Froude number of the upstream of the flume is less than 0.4,the upstream backwater height is between 1.68-4.88 cm,and the critical submergence of the flume is 0.80-0.92.(2)The numerical simulation results are basically consistent with the actual test results.It is basically reliable to use the computational fluid dynamics simulation method to study the measuring flume.The Froude number in front of the flume is less than 0.5,which is basically consistent with the test.The upstream flow is gentle,which is beneficial to reduce the measurement error of stagnation point water depth.The turbulent kinetic energy dissipation of the portable primary and subsidiary fish-shaped flume is concentrated in the area near the side wall and bottom of the channel.The maximum velocity of the two outlets located in the center of the flume occurs at the midpoint of the water level.Because the water flow is divided by the mother column,it collides and converges again at the outlet,and the local head loss of the measuring flume is large.To optimize the flow pattern in a primary and subsidiary fish-shaped measuring flume and minimize head loss,it is important to choose primary and subsidiary measuring water columns that have an appropriate length-width ratio and a reasonable distance between the sub-column and the mother column.(3)Compared with other U-shaped channel portable measuring flumes,the water column structure of the primary and subsidiary fish-shaped measuring flume has a good streamline shape,and the four outlets ensure the smooth flow of water in the flume.The hydraulic characteristics of the six different structural flumes show the following characteristics: the upstream backwater level of the elliptical flume is the highest,followed by the plate-column combined flume,the fish-shaped flume,the cylindrical flume,the V-tailed cylindrical flume,and the primary and subsidiary fish-shaped flume is the lowest.The order of water head loss is as follows: the plate-column combined measuring flume has the largest head loss,the oval measuring flume,the cylindrical measuring flume,the V-tail cylindrical measuring flume,the fish-shaped measuring flume,and the primary and subsidiary fishshaped measuring flume.The Froude number in front of the six flumes meets the requirements of flow measurement.Under the same working conditions,the upstream backwater height generated by placing the primary and subsidiary fish-shaped measuring flume in the channel is low,resulting in the smallest head loss.The elliptic curve can be used to keep the upstream flow stable on the water surface of the water column.The diffusion section after the throat can be designed as a curved tail to reduce the head loss.If the height of the upstream backwater meets the necessary criteria,the critical submergence can be enhanced by suitably extending the throat length.