Free surface vortex control is very important in a pump sump system.Because air absorbed by surface vortex induces noise, vibration, and cavitation corrosion on pumping system.In this study, change of free surface vortex and air absorption in a pump intake have been investigated by a VOF method with unsteady multiphase flow model in order to represent the behavior of the free surface vortex exactly.Homogeneous free surface model is used to apply interactions of air and water.The results show that the free surface vortex motion can be visualized using the isotropic surface at air volume fraction 1％～5％.The vortices make an air column from the free surface to the pump intake and are created and destroyed repeatedly in case of asymmetric intake.And it was found that tree surface vortex can be controlled by installing curtain walls.
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