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输水明渠壅水状态断面流速特性三维仿真研究

Three-dimensional Simulation of Cross-section Flow Velocity Characteristics of Open Water in Open Channels

  • 摘要: 传感器技术的发展给渠道流量测量领域带来了新的契机,目前多数测流设备主要通过测量点流速来推求渠道断面的流量。但在渠道中由于壅水作用的影响,同一个断面处的流速分布随下游水深变化而变化。为探索不同下游水深边界条件下输水明渠的断面流速分布特性,采用FLOW-3D进行三维建模仿真,选取平原灌区内一典型梯形渠道中100 m渠段,针对不同下游壅水条件进行恒定流三维数值模拟。通过研究不同下游水深条件下的断面流速分布,分析了采用固定水面流速系数可能导致的流量误差,并根据水面流速系数的变化规律,提出了在渠段下游壅水高度小于20 cm时采用率定的水面流速系数推算流量误差可满足量水精度要求(误差小于±10%)。还针对仿真数据进行拟合得到水面流速系数关于水深的曲线,并利用该曲线对水面流速系数进行修正,结果表明测流误差可减小到1.4%以内。最后分析了使用雷达技术测水面流速时,在保证测流误差不大于10%条件下应选取的最小测点数。

     

    Abstract: The development of sensor technology has brought new opportunities to the field of channel flow measurement. At present,most flow measurement equipment mainly estimates the flow of the channel section by measuring the flow velocity at the point. However,in the channel,due to the effect of backwater,the velocity distribution at the same section changes with the downstream water depth. In order to explore the cross-section flow velocity distribution characteristics of open channel under different water depth boundary conditions,this paper uses FLOW-3D for 3D modeling and simulation. A 100 m canal section in a typical trapezoidal channel in the plain irrigation area is selected to perform constant flow for different downstream backwater conditions. By studying the cross-section velocity distribution under different downstream water depth conditions,the possible flow error caused by using a fixed surface velocity coefficient is analyzed,and according to the variation law of the water surface velocity coefficient,a fixed-rate method is proposed when the height of the backwater below the channel is less than 20 cm water surface velocity coefficient can be used to estimate the flow error(the error is less than ± 10%). This paper also fits the simulation data to obtain the curve of the water surface velocity coefficient with respect to the water depth,and uses this curve to modify the water surface velocity coefficient. The results show that the measurement error can be reduced to within 1.4%. Finally,it analyzes the minimum number of measurement points that should be selected when the radar technology is used to measure the water surface velocity,while ensuring that the measurement error is no more than 10%.

     

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