起伏管道内水流冲击滞留气团的三维动态特性模拟

Three-dimensional simulations on dynamic characteristics of flow impacting entrapped air pocket in undulating pipeline

采用三维CFD方法对起伏管道内水-气耦合作用的过程进行建模和模拟,研究气团压缩-膨胀-变形的三维动态特性.在考虑气团压缩性、水体弹性基础上,采用Standard k-ε、RNG k-ε和Realizable k-ε这3种湍流模型进行模拟研究,并将三维计算结果、现有一维模型计算结果与试验结果进行了对比分析.结果表明:与一维模型相比,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气水形态变化和压力波动;Standard k-ε湍流模型能够较好地模拟压力峰值和波动周期,RNG k-ε、Realizable k-ε湍流模型次之;整个过程中,水-气两相互相掺混,水-气交界面自由变化,并不垂直于管道中心线,与管道中心线呈一定的夹角存在;三维CFD计算结果可以很好地模拟较短长度气团的动态特性变化.

Transient flows in a filling undulating pipeline with entrapped air pocket are complicated,and may cause abnormal pressure surge.Three-dimensional CFD(3D)method was introduced to simulate the water-air interaction,and to investigate the 3D dynamic characteristics of the compression-expansion-deformation entrapped air pocket.On the basis of including the compressibility of air phase,the 3D method considered the elasticity of water phase.Three kinds of turbulence models(Standard k-ε,RNG k-ε,and Realizable k-ε)were used in the simulations.The comparisons of the results calculated by the proposed 3D CFD model and existing one-dimensional(1D)model,and the experimental results were conducted here.Results show that compared with 1D model,3D CFD model can better simulates the transient pressures and air-water profiles in the filling undulating pipeline.Moreover,Standard k-εturbulence model more accurately simulates the pressure peaks and fluctuation periods compared with RNG k-εand Realizable k-εturbulence models.During the filling process,the water-air two-phases are mixed with each other,and the water-air interface changes freely,which is not perpendicular to the center line of the pipeline,and has a certain angle with the center line of the pipeline;the 3D CFD calculation results can well simulate the dynamic characteristics of short length air pockets.