大真空度长距离正虹吸管道水气两相流动水力特性研究

Siphon pipe with the shape like hump is widely used in the short distance water delivery engineering. The study of long distance siphon pipe with large vacuum is few. The largest vacuum of siphon pipe is more than 6 meters water column, and the horizontal pipe's length is greater than 500 meters. On the basis of previous experimental research, the similarity principle between the prototype and model of gas-liquid flow in large vacuum siphon pipe is analysed and established. Based on the continuity equation and momentum conservation equations, and combined with the operation characteristics of large vacuum in the pipe, the head loss calculation models of different flow patterns are established. Meanwhile, the gas-liquid's flow resistance is researched by the system experiments, and the interaction among the gas, liquid, and the wall of the pipe is studied. Considering the pipe with characteristics of large vacuum, the gas-liquid flow model is established based on the gas-liquid two-phase flow dynamics theory, and it is combined with the turbulence model to simulate two-phase flow characteristics. With the combination of theoretical analysis, experiment system and numerical simulation, the water & gas flow dynamic characteristics of the long distance siphon pipe with large vacuum are obtained, and the head loss mechanism of the pipe is ascertained, and calculation of frictional resistance coefficient and flow coefficient are provided. The research results of this project are expected to provide theoretical basis for design and management of long distance siphon pipe with large vacuum, and enrich the theory of model experiment similarity and the one of pressure pipeline hydraulic calculation.

虹吸输水多应用于短距离输水工程，且多采用驼峰式虹吸管。对于真空度大于6米水柱且真空水平管段长度大于500米的长距离大真空度正虹吸管道输水的形式及研究很少。本项目拟在前期研究基础上，运用相似模化原理分析和建立长距离大真空度正虹吸管道内水气两相流动的原型、模型相似准则；基于连续方程和动量守恒方程，结合大真空度运行的特点提出并建立水气两相流管道水头损失计算模型。通过系统实验研究流型不同时水气两相的流动阻力，分析水气相间相互作用及其与管壁的相互作用。运用气液两相流动力学理论，建立大真空度条件下管道水气两相流动模型，并结合紊流模型模拟两相流动特性。通过理论分析、系统实验和数值模拟研究，获得大真空度长距离正虹吸管道水气两相流动水动力特性，探明其不同于满流有压管道的能量损耗机理，推导沿程阻力系数和流量系数计算公式。其研究成果可望为工程设计与运行提供理论依据，丰富和完善模型相似理论和有压管道水力计算理论。

真空度大于5米水柱且中行管段采用非驼峰式的大真空度正虹吸管道输水的形式及研究很少。本项目通过系列试验研究了流型不同时不同管径、不同坡度的大真空度虹吸管路内的水气两相流动特性，应用方程分析法推导出适用于大真空度正虹吸管道伪空化现象的原、模型相似准则。基于试验结果获得流型、坡度、管径、真空度对管道过流能力、压降、稳定运行时间及含气率的影响规律，揭示气体存在对管道过流能力和水头损失的影响机理。根据气液两相流动力学理论建立数学模型，对虹吸管内含有不同直径气泡时的水气两相流动特性进行了数值模拟，获得气泡运动行为对相间作用力的影响。.通过理论分析、系统实验和数值模拟研究，得到以下成果：（1）真空度大于2m水柱时，虹吸管内气液两相流现象为伪空化现象。（2）获得适用于真空有压输水管伪空化现象的水力模型相似准则：原、模型的佛汝德数、掺气率及任意断面上的压强相等。（3）气液两相流流型根据流速大小可分为气泡流、过渡流和气团流。流速大于0.4m/s时为气泡流，流速小于0.4m/s时出现过渡流和气团流。坡度改变对流型没有影响。（4）推导出考虑坡度、截面含气率和水头差影响时的气泡流和气团流流型的流量系数和沿程阻力系数公式。（5）气体对虹吸管路水力特性影响机制因流型不同而异。气团流时总水头损失和流量系数计算中应计入气囊引起的局部水头损失，气泡流时可忽略不计。坡度越小时气囊引起的局部水头损失占总水头损失的比重越大，平坡时达到最大。（6）当含气率α≤8%时，沿程阻力系数λm与含气率成呈正比，与Re数呈反比，与坡度无关；当α＞8%时，λm与坡度和Re呈反比，与α呈正比。（7）中行管坡度对管路能否稳定运行影响显著，平坡布置时的稳定虹吸时间最短。建议将虹吸管路按正坡布置，且出口采用淹没出流。（8）气液相间阻力随气泡雷诺数增大而增大，振荡位移随其增大而减小，气泡的形变比随气泡尺寸的增大而减小，且随水流雷诺数增加而增大。气泡越小愈不容易聚合成气团。