LES analyses of the air-core vortex in intake flow field of pumping station

Air-core vortex is a universal and attention-getting phenomenon in intake flow field of pumping station. Due to the difficulties and complexities of two-phase flow of the air-core vortex, the Coupled Level-Set and Volume-of-Fluid (CLSVOF) method is adopted in the simulation, and a horizontal intake pipe in pump sump was calculated. Results of the simulation were consistent with that of experiment. The air-core vortex is successfully reproduced in the simulation, and four stages during its formation is observed. At the early stage of the simulation, vortices generated in the vicinity of the free surface are gathered in the stagnation region above the pipe intake. The intensity of the gathering vortices increases due to the stretching effect of ω_y (vertical vorticity component), and move toward to the pipe intake due to the downward flow motion of the stagnation region. Furthermore, air-core vortex meandering is observed from the time series of instantaneous vortex motion, and quasi-periodicity is founded in its meandering, which is caused by the quasi-periodic characteristic of the velocity filed. The dominant frequency (fD/v_D ) of coordinate x of the air-core vortex center is around 0.0096, and coordinate z is around 0.0191.