Numerical study on gas–liquid separation of two-phase swirling flow based on the Eulerian-Eulerian approach and RSM turbulence model

Abstract

The steam-water separation package in U-tube steam generator is designed to minimize water content to ensure turbine safety. However, the design of this key component still relies on experiments and trial-and-error methods due to the lack of comprehensive analytical success. The two-phase flow inside an axial swirler is modeled by the Eulerian-Eulerian multiphase flow approach, in which both gas and liquid phases are considered as continuous and coupled to each other. The choice of an appropriate turbulence model significantly impacts on the accuracy of simulation results. The simulation performance of three advanced swirling turbulence models on the gas–liquid interface downstream of the swirler is analyzed. The void fractions along the axial cylinder sections above the swirl vanes are compared with the corresponding experimental air core diameter data from the literature. It is found that the void fraction calculated with RNG k-ε and Realizable k-ε turbulence models decreases monotonously with the axial height above the swirl vanes, whereas the RSM model shows an initial decrease followed by an increase. The RSM model’s results align well with experimental data, particularly in predicting the turning point of void fraction. Adequate grid coverage in the boundary layer is essential to capture the gas–liquid interface due to the very thin liquid film. To obtain the better prediction of gas–liquid swirl flow, the RSM turbulence model and appropriate boundary grid coverage are recommended.