含有窝气的虹吸整流输水管道水力损失计算与试验研究

为了研究输水管道窝气对管路水力损失的影响,对1套包含小坡度长下坡段的管路系统分别在自然重力进流、低虹吸进流、高虹吸进流(虹吸进口装有整流装置)条件下进行管道满流与带气试验测量.创新建立窝气阻力系数β定量表示窝气阻力造成的水力损失增加,提出了整个管路窝气阻力系数的计算公式.基于试验数据分析了不同进流方式在带气与不带气条件下的管路阻力特性,并验证了窝气形成气阻机理的存在.研究结果表明:输水管道窝气会减小管道有效过流面积,造成管路水力损失显著增加,且管道的高低起伏越多,管路中弯头、变径管件数量越多,管道窝气阻力系数β越大;虹吸式进流在整流装置的作用下,较自然重力式进流会降低管道摩擦系数,并且高虹吸下的水力摩擦系数最小;通过合理设计,虹吸整流装置的多孔结构可以根据管道流量的大小不断自动调节其自身的阻力和开度,有效控制管道入口进气.

Computational and experimental study on hydraulic loss in water pipeline with entrapped air and siphon head

To explore the influence of entrapped air in a water pipeline on its hydraulic loss, a small slope siphon test rig, which is an undulating pipe with a long downward sloping pipeline, was built. Experiments were carried out under different inlet conditions, namely natural inlet, low siphon inlet and high siphon inlet(with a multi-hole siphon head). At first, an entrapped air resistance factor β was innovatively introduced to account for the increase of hydraulic loss due to the entrapped air in a pipe, and the formulas for determining the flow resistance in the pipe were deduced. Then, the flow resistance characteristics of the pipe were analyzed based on the experimental data obtained under diffe-rent inlet conditions with and without entrapped air. The mechanism for entrapped air to increase flow resistance was verified. The results show that the entrapped air can reduce the effective flow cross-sectional area and increase the hydraulic loss in the water pipeline considerably, and the more the numbers of undulations and pipe fittings in the pipeline, the larger the entrapped air resistance factor β. Compared with natural inlet, a siphon inlet can reduce the hydraulic friction factor of the pipeline, and the hydraulic friction factor is the smallest for the high siphon inlet. If a multi-hole siphon head is designed properly, the multi-hole structure can automatically adjust its own resistance and opening according to the flow rate in the pipeline, then can effectively control the air flow rate at the pipeline inlet, eventually, reduces the hydraulic loss in the pipeline.