Three-dimensional simulations on dynamic characteristics of flow impacting entrapped air pocket in undulating pipeline
LU Kunming1, ZHOU Ling1*, CAO Bo2, LIU Deyou1, WANG Huan1
1. College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing, Jiangsu 210098, China; 2. State Grid Xinyuan Hydropower Company Limited, Jiande, Zhejiang 311600, China
Abstract：Transient flows in a filling undulating pipeline with entrapped air pocket are complicated, and may cause abnormal pressure surge. Three-dimensional CFD method was introduced to simulate the water-air interaction, and to investigate the three-dimensional(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, and 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 mo-del can better simulates the transient pressures and air-water profiles in the filling undulating pipeline. Moreover, standard k-ε turbulence model more accurately simulates the pressure peaks and fluctuation periods, than RNG k-ε and Realizable k-ε turbulence models. During the filling process, the water-gas 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 three-dimensional CFD calculation results can well simulate the dynamic characteristics of short length air pockets.
