梯形喉口无喉道量水槽设计及其水力性能模拟与试验

Design of trapezoidal cut-throated flume and its hydraulic performance simulation and test

为了解决灌区普遍存在的通过增大水头损失来提高测流精度的问题,该文提出了一种具有梯形喉口的无喉道量水槽,并给出了量水槽参数与渠道尺寸的比例关系。该文在原型试验基础上,通过Flow-3D软件对过槽水流进行了数值模拟,分析了测流过程中水流流态、纵向时均流速分布、水头损失、湍动耗散沿程变化以及测流精度。研究结果表明:纵向时均流速分布和水流流态的模拟值与实测值最大相对误差均不超过10%,其模拟结果与实测结果较为吻和;基于临界流原理和能量守恒推出的水位流量关系式,进一步回归分析得到测流公式,其计算值与实测值最大相对误差为9.21%,满足量水精度要求;水头损失随着流量增大而增大,当流量大于45 L/s时,增大趋势明显变缓;最大水头损失不超过上游总水头10%,相比长喉道、巴歇尔、抛物线形量水槽水头损失较小。该研究可为灌区渠道量水设施设计提供参考。

Accurate flow measurement is a fundamental component of water management. Owing to their good hydraulic characteristics and easy maintenance, trapezoidal channels have been widely used in terminal water convey systems of China. Previous research indicated that the measuring flume is one of the most accepted and used structures for water discharge measurement. We designed trapezoidal cutthroat flumes to measure the discharge in terminal trapezoidal channels. These flumes can improve flow measuring accuracy without sacrificing water head. We also researched the relationship between channel specification and the flume＇s parameters for its application. Based on the RNG k-ε three-dimensional turbulence model along with the TruV OF technique, experiments and corresponding simulations were performed for 14 working conditions on the trapezoidal cut-throat flume with discharges up to 75 L/s to determine its hydraulic performance. Hydraulic performance of the flume obtained from simulation analyses was later compared with observed results based on time-averaged flow field, flow pattern, and velocity distribution. The comparison yielded a solid agreement between the results from 2 methods with the relative error below 10%. On the basis of reliable consequences simulated numerically, analyses of hydraulic performances in detail were carried out. The flow in the upstream of the flume was slow flow with almost parallel flow direction, then the water surface was gradually declined along the contraction segment and the water on both sides tended to converge at the center line. Owing to the severe contraction of the throat section, the water surface near the downstream of the throat section was dramatically declined and the lowest point appeared. From the posterior part of the diffusion section, the water depth gradually increased to the downstream depth with the water depth uniformly distributed in the horizontal section. By analyzing the variation of velocity and total head along the flume under different discharges, it was concluded that both velocity and total head loss accelerated dramatically near the throat. The turbulent dissipation was concentrated in the area near the wall and the bottom of the flume. Regression models developed for upstream depth versus discharge under different working conditions were satisfying with the relative error of 9.21%, which met the common requirements of flow measurement in irrigation areas. Furthermore, the maximum water head loss of the trapezoidal cut-throat flume was less than 10% of the total head. Compared with long-throat flumes, Parshall flumes and parabolic flumes, the head loss of trapezoidal cut-throat flume in trapezoidal channels was less. The three-dimensional turbulence model along with the TruV OF technique allowed one to reproduce the hydraulic characteristics of flow through trapezoidal cut-throat flume in trapezoidal channels. Due to the shorter time demand and lower cost of numerical simulations, compared to experimental studies in predicting the hydraulic characteristics, the simulation of the flow in trapezoidal cut-throat flume in trapezoidal channels based on a properly validated model provided the flow characteristics of these flumes for various flow configurations encountered in the terminal channel. All in all, it is concluded that the trapezoidal cutthroat flume has the advantages of simple structure, low price and high accuracy, plus low head loss. This study provides a reference for the flow measurement of terminal channels in irrigation areas.