侧渠底高对分水口水力特性影响数值模拟研究

Numerical simulation of influence of side channel bottom height on hydraulic performance of bleeder

目前对灌区分水口水力性能的研究多集中在主渠和侧渠底部高程相等的情况下,对于普遍存在的侧渠底部高程高于主渠时的分流特性缺乏系统研究。该文在试验基础上,利用FLOW-3D软件对侧渠不同底高、主渠来流量的矩形渠道分水口进行了数值模拟研究,将主渠各断面水深、流速的模拟值与实测值进行对比,发现流速变化与实测值变化规律基本一致,相对误差均小于10%,利用FLOW-3D对分水口进行数值计算具有合理可信性。结果表明:分水口处的水面波动受主渠来流的影响,流量越大,波动越大;高于侧渠底高的水流会对低于侧渠底高的下层水流产生影响,使下层水流具有向上的流速分量,参与分水口分流;同一主渠来流量下,随侧渠底高的增加,侧渠进口断面最大流速和水深逐渐减小;侧渠进口断面靠近上游端的区域湍动较大,而在下游端靠近底部湍动能值较小。研究为灌区配水及水量控制提供了参考依据。

In recent years,most researches focus on the same height at the bottom of both main and side canal to study the hydraulic performance of water diversion.However,in practice,the height of main and side canal bottom are different in most irrigation districts.In this paper,the effect of the height of the side canal bottom on the hydraulic performance of bleeder was studied.The prototype test was carried out in Northwest A&F University in Yangling,Shannxi of China.In the prototype test,both the main channel and side channel were rectangular.The length of the main channel was 12-m long and 0.46-m wide.The length of the side channel was 2.5 m,and the width was adjustable in the range of 0.14-0.46 m.The elevation of the side channel was 0.06,0.08 and 0.1 m higher than the bottom elevation of the main channel.A total of 8 flow sections were set up,5 of which were at the water inlet.In order to analyze the water surface variation at the water diversion of the main channel,3 measuring points at section I,section II,section III,section IV,section V,section VI were taken.The 3 measuring points were on the center line and 5 cm away from the wall of the main channel on both sides.The variables in the test were the side channel width and the flow rate.The water depth and velocity were determined at the measuring point.To eliminate the influence of boundary conditions,this study simplified the experimental channels.The width of the simulated main and side channels was the same as the actual width of the main and side channels.However,the lengths of the main and side channels were correspondingly extended on the basis of the actual channel length,which were 12 and 5m respectively.Because the flow field near the water-diversion changed drastically,the grid interval at the area was decreased,the cell length was 0.01 m,the remaining area cell grid was 0.02 m,and the total grid number was about 900000.In the channel model,the inlet boundary of the main channel was set to several volume flow rates,which were 19.96,25.2,30.2,36.5 and 45.32 L/s,respectively;the outlets of the main channel and the side channel were set to be free;the side wall of the channel was selected to have no sliding wall;the air above the free surface was air,and the relative pressure was 0.Based on experiments,FLOW-3D was used to simulate and calculate several flow rate and heights on the rectangular channel water diversion,compared to the measured water depths and velocity.The results showed that the variation of velocity was basically consistent with the measured value and relative error was less than 10%.It was reliable to make numerical analysis on water diversion by using FLOW-3D.The numerical simulation showed that the fluctuation of water surface at the water diversion was affected by the flow rates from the main channel.With the increasing of the bottom height,the maximum velocity and water depth of the side channel inlet section gradually decreased.At the entrance of the side channel,the turbulent kinetic energy near the upstream end was large,while at the downstream end of the branch,the turbulent kinetic energy near the bottom was small.The study provides information on water distribution and water-quantity control in irrigation area.