摘要
根据北方灌区渠道底坡缓且灌溉水流多泥沙的现状,该文针对U型渠道设计了平板量水装置。为了探索不同尺寸悬垂薄平板在明渠水流冲击作用下的水力学特性,确定流量与平板偏转角度之间的关系。分析水流流态,将渠道运动水流分为3部分,对平板部分水流应用闸孔淹没出流公式,建立流量计算模型,得出流量与角度的半经验关系式。对流量系数计算模型中的待定系数进行估计,得到了统一形式的流量公式。U型平板测流范围为9~44L/s,经验证,计算流量与实测流量之间最大相对误差为6.9%,平均相对误差为3.2%,其中收缩比0.547、0.439平板测流相对误差均小于5%,满足灌区量水要求。同一收缩比板型,相对水头损失随着流量增大而减小,不同收缩比板型,相对水头损失随着板型收缩比增大而增大,除收缩比0.715平板在小流量(本试验大约为10L/s)测流时,相对水头损失比在10%以上,其余平板测流时相对水头损失均小于10%,其中收缩比为0.439和0.337平板最大水头损失不超过上游总水头6%。经过综合分析,选择0.547到0.439为平板最佳收缩比测流范围。研究可为灌区量水设施的改进提供依据。
In view of lack of effective regional water measuring facilities for gentle slope canal with silt current in irrigation areas of northern China, a portable U-shaped flat water measuring device was proposed as a flow water measuring equipment in the field. This study was to investigated its hydraulic performance of flat water measuring facilities based on prototype test. The prototype test was carried out in Northwest A & F University in Yangling, Shannxi of China. In order to explore dynamic characteristics and deflection phenomenon of a draping thin plate under the impact of open channel flow, the relationship between discharge and deflection angle of the plate was determined. The flow pattern was analyzed, and the moving water flow was divided into 3 parts. The formula for calculating the outlet flow of gate was applied to the flow relative to measuring device, and the flow calculation model was established. The undetermined coefficients in the flow coefficient calculation model were estimated and a unified formula for flow rate was obtained. The flat shape was made up of a rectangle and a semicircle, arc radius were respectively 16, 12, 10 and 8 cm, and the corresponding contraction ratios were 0.715, 0.547, 0.439 and 0.337. The measuring device was installed at 5.0 m far from the inlet of upstream of U-shaped channel. The base slope of the channel was 1/2 000. The triangular weir was installed at the end of the downstream of the channel to measure current flow. A total of 10 sections were used to observe the flow characteristics. The current range of U plate measuring device was 9-44 L/s(9 work conditions for each contraction ratio). The results from the prototype experiment was used to compute model parameters and validate the simulation results. The result showed that the maximum relative error between the measured flow rate and the calculated flow rate was 6.9%, with an average relative error of 3.2%. For the contraction ratio of 0.439 and 0.547, the plate flow measurement errors were less than 5%, which met the water measured requirement of irrigation area. It indicated that the current calculation model had a high accuracy. With the same contraction ratio, the relative head loss ratio decreased with the increase of flow rate, the relative head loss ratio increased with the increase of plate contraction ratio. The ratio of relative head loss was more than 10% when the plate contraction ratio was 0.715 plate at the low flow rate(about 10 L/s in this test), and the relative head loss ratio of the remaining plate was less than 10%. Besides, the maximum relative head loss of plate contraction ratio of 0.337 and 0.439 was not higher than 6%. After comprehensive analysis, 0.547 to 0.439 were chosen as the best plate contraction ratio. In practical application, devices such as wind prevention, instrument protection should be installed externally to reduce the influence of wind load and meteorological factors on measurement accuracy. The trash gate should be installed along the upstream to intercept the floating objects such as weeds. When this device was not used for measuring discharge and before the channel froze in winter, the device should be turned up to the vertical statement, which didn’t affect the channel water delivery. According to different sizes of U-shaped canals, the appropriate bottom arc radius should be selected to make the plate.
作者
王文娥
张维乐
胡笑涛
Wang Wen’e;Zhang Weile;Hu Xiaotao(Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas, Ministryof Education, Northwest A & F University, Yangling 712100, China)
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2019年第13期84-90,共7页
Transactions of the Chinese Society of Agricultural Engineering
基金
公益性行业（农业）科研专项（201503125）
“十三五”国家重点研发计划项目（2016YFC0400203）
关键词
流量
渠道
角度
渠道闸孔出流
流量系数
水头损失
flow rate
canal
angle
canal gate hole outflow
discharge coefficient
head loss
