| In view of the current situation of irrigation area in China,a streamlined measuring flume-rudder-like measuring flume is designed based on the shape of underwater submarine,which has the characteristics of accurate measurement,high applicability and small flow resistance.Six streamline curves were selected by the linear fitting method of the rotary body given by the accurate mathematical expression and the discrete shape coordinate shape value,and the flow characteristic parameters of the constructed different linear flumes were studied by the numerical simulation method,so as to understand the hydraulic characteristics of the flow through the flume in depth,determine the optimal shape of the flume by comparison,and construct and design the rudder-like flume.On this basis,the hydraulic performance of rudder-like flume with different contraction ratios and flow rates was experimentally studied to obtain the hydraulic characteristics of flume.At the same time,the flow formula of rudder-like flume is established based on dimensional analysis method,and the accuracy of the flow formula is analyzed.The main conclusions are as follows :(1)The influence of upstream contraction section and downstream diffusion section on the flow hydraulic characteristics of the flume was studied.The contraction section has obvious influence on the critical depth of throat section and the backwater height of upstream channel.The smaller the curvature radius of contraction section,the larger the critical depth and the smaller the backwater height.The downstream diffusion section mainly affects the downstream flow pattern and head loss of the flume.The larger the curvature radius of the diffusion section,the smaller the head loss.(2)Based on the streamline curve selected by linear fitting,six types of volumetric flume are designed and constructed,namely EE type,EP type,EA type,NST type,KKS type and CBD type.The flow characteristics of the flume in rectangular channel are simulated and studied.The upstream Froude number is less than 0.5 in the test flow range,forming a stable slow flow;backwater height is not more than 4 cm,head loss is less than 3.5 cm,to meet the application requirements of existing channels;the average error between calculated flow and simulated flow is 2.51 %,and the accuracy of simulated flow is high.The hydraulic characteristics of the KKS rudder-like flume under the test flow condition were compared and analyzed.It was found that the velocity distribution of the KKS rudder-like flume was uniform and the flow pattern was stable.The average error between the calculated flow and the simulated flow was only 1.73%,and the accuracy of the simulated flow was the highest.The maximum head loss is only 3 cm,and the comprehensive hydraulic performance is the best,which can be used as the basic shape for constructing rudder-like flume.(3)Based on the optimal shape,a rudder-like flume with throat contraction ratio ε of0.45～0.67 was constructed to study its hydraulic performance.The results show that the flow in the rudder-like flume is stable and smooth under the conditions of test flow rate and contraction ratio,and the Froude number of upstream flow is less than 0.5,which meets the flow measurement standard.the mean backwater height before the trough was 4.2 cm,and the maximum was 8.7 cm,which met the specification requirements;the mean value of critical submergence is 0.83,and the maximum value is 0.92,indicating that the groove has a large free outflow range.The head loss of rudder-like flume is not more than 8 cm within the test flow range,and increases with the increase of flow rate and decreases with the increase of contraction ratio.When the contraction ratio ε is 0.45,the head loss is 2.5cm～7.9cm;when the contraction ratio ε is 0.5～0.67,the head loss is 0.9cm～6cm.The error analysis between the calculated flow rate and the measured flow rate by the critical flow formula shows that under the experimental conditions,the maximum error is 4.98%,the minimum error is 0.36%,and the average error is 3.1%,with high flow measurement accuracy.By comprehensively analyzing the influence of contraction ratio on the hydraulic characteristics of the rudder-like measuring flume,it is found that when the contraction ratio is between 0.5 and 0.67,the flow measurement accuracy of the rudder-like measuring flume is higher,the backwater height and head loss are smaller,and the hydraulic performance is better.(4)The flow formula of rudder-like flume is established by dimensional analysis method.The formula meets the dimensional harmony.Compared with the measured flow,the maximum relative error is only 4.90%,and the average error is 2.25%.It has high accuracy,simple form and convenient use,and can be used as the basic formula for the flow calculation of rudder-like flume. |
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