水平-竖直管道内水流冲击滞留气团的三维数值模拟研究

Three-dimensional Numerical Simulation of Water Impacting Entrapped Air Pocket in Horizontal-vertical Pipeline

水平-竖直管道内水流冲击滞留气团现象复杂且可能产生异常压力波动,本文采用三维CFD方法对其水气耦合作用过程进行建模和模拟。在考虑气团压缩性基础上,考虑了水体弹性,采用两种湍流模型(Standard k-ε、RNG k-ε)进行模拟研究,并将三维计算结果与实验结果进行了对比分析,研究气团长度、管壁粗糙度等参数的动态变化过程。结果表明:所采用的三维CFD模型能够较准确地模拟起伏管道内水流冲击滞留气团瞬变过程中水气形态变化和压力波动;系统最大压力随气团长度减小而增大,随入口压力增大而增大,且增值远大于系统入口压力增值;RNG k-ε湍流模型适用于长气团以及短气团、高压力入口条件,Standard k-ε湍流模型适用于短气团、低压力入口条件;管壁粗糙度对瞬态压力的影响与气团长度有关,不同压力峰值对管壁粗糙度的敏感性不同。

The phenomenon of water flow impacting and entrapped air mass in horizontal-vertical pipeline is complex and may produce abnormal pressure fluctuations.A three-dimensional CFD method is used to model and simulate the water-air coupling process.By considering the compressibility of air mass and the elasticity of water body,two turbulence models(Standard k-ε,RNG k-ε)are used to conduct the simulation study and the simulation results are compared with the experimental results to study the dynamic changes of the length of air mass and the pipe wall roughness.The results show that,(a)the three-dimensional CFD model can accurately simulate the changes of water vapor shape and pressure fluctuations during the transient process of the impingement of retained air mass in the undulating pipeline;(b)the maximum pressure of the system increases with the decrease of air mass length and increases with the increase of inlet pressure,and the increase of maximum pressure is much greater than the increase of system inlet pressure;(c)the RNG k-εturbulence model is suitable for the conditions of long or short air masses,and high inlet pressure,and the Standard k-εturbulence model is suitable for the conditions of short air masses and low inlet pressure;and(d)the effect of pipe wall roughness on transient pressure is related to the length of air pocket,and different pressure peaks have different sensitivities to pipe wall roughness.