Research On Shape Optimization And Hydraulic Performance Of Myring Streamline Measuring Flume

China’s agricultural water consumption is huge,but currently the effective utilization coefficient of irrigation water in farmland is still low.It is still necessary to vigorously develop water-saving agriculture.Studying water measurement technologies that are easy to promote and suitable for the final channel of irrigation areas is of great significance for rational allocation of water resources,achieving water conservation,and planning water use.The bionic streamline structure is widely used in the field of underwater vehicles.Because the blocked state of the measuring flume in the channel flow field is similar to the resistance of the submersible when it is diving,this paper uses the structural characteristics of the submersible for reference to design the shape of the measuring flume and explore the optimal shape of the measuring flume with the least resistance.Based on three streamline curve structures widely used in the field of submersible,the flume model is established,and the streamline structure is compared and selected through numerical simulation.Then an optimization platform based on neural network and genetic algorithm combined with CFD method is established to further optimize the Myring streamline with good performance and strong plasticity.The optimization results are applied to the structural design of the flume,and the optimization of Myring streamline flume is proposed,Through the combination of field test and numerical simulation,the critical submergence degree,flood height,head loss,flow measurement accuracy,Froude number,streamline characteristics of internal flow field,velocity distribution and turbulent energy dissipation rate of the optimized Myring streamline flume under different flow rates,different shrinkage ratios and two layout modes are analyzed,providing a basis for the promotion of the flume in irrigation areas.The main research results are as follows:(1)First,verify the accuracy of the numerical simulation method based on the test results of the wing shaped portable flume in the trapezoidal channel that has completed the test,and verify the reliability of the simulation.Then,compare three streamline based on the numerical simulation method,and select Myring streamline with small head loss,wide flow measurement range and good linear plasticity to design the flume,In order to reduce the head loss and the height of Yongshui River,the streamline measuring flume was further optimized based on BP neural network and NSGA-Ⅱ genetic algorithm combined with CFD method,and the optimal linear parameters were obtained.The optimization of Myring streamline measuring flume was proposed.(2)Based on the optimized Myring streamline,the test models with different shrinkage ratios were constructed,and the flow measurement tests under 6 shrinkage ratios and 9 flow rates were carried out in the rectangular channel in two layout modes of side shrinkage and portable.The results show that the critical submergence degree is larger when the contraction ratio is 0.58～0.66 under the two layout modes of optimized Myring streamline measuring flume.When the contraction ratio is 0.50 and 0.54,the critical submergence is relatively small,the water depth is high,and the head loss and proportion are large.The upstream Froude number under all operating conditions is between 0.25 and 0.42,meeting the flow measurement standards of the irrigation area’s measuring tank.There is not much difference in hydraulic performance between the two arrangement methods,but the hydraulic performance is slightly better when using side contraction arrangement.(3)Based on the CFD method,the internal flow field of the optimized Myring streamline measuring flume under different shrinkage ratios,different flows and two layout modes was analyzed in depth,and different shrinkage ratios were added to expand the analysis range and save test time.The results show that the simulated flow pattern of the optimized Myring streamline measuring flume under the two arrangements is basically consistent with the actual flow pattern,and the simulated water surface profile is consistent with the experimental observation results.The results further verify the accuracy of the simulation.The Froude number along the flow direction develops from stable to increased,and then to reduced to stable,and shows a single peak distribution.The smaller the contraction ratio,the higher the Froude number peak value,the deeper the transformation of kinetic energy,and the greater the head loss.However,when the contraction ratio is too large,critical flow cannot be generated.Combined with the analysis of test data,optimize the Myring streamline measuring flume in practical use,The recommended shrinkage ratio range for both arrangement methods is 0.58 to 0.62.A dimensionally harmonious flow formula has been established based on the dimensional method and critical flow principle.When arranged in a side contraction manner,the average absolute value of flow measurement error is 1.16%,and when arranged in a portable manner,the average absolute value of flow measurement error is 1.80%.Both arrangement methods have high flow measurement accuracy.(4)Based on FLOW-3D software,the flow field of rudder like measuring flume,wing like measuring flume and optimized Myring streamline measuring flume with contraction ratio of 0.60 in rectangular channel was simulated and calculated.The results show that the optimized Myring streamline flume has the advantages of small height of flood water,smooth flow,wide free outflow range,high critical submergence and small head loss.It has broad application prospects in plain irrigation areas and irrigation canal systems with poor water head conditions in China.