A numerical study on the behavior of free surface vortices occurred in a pump sump was carried out. Free surface flow in an intake channel was solved by using finite volume method for RANS equations with k‑wSST turbulence model. A VOF multiphase model and the open channel model were used to solve the multiphase flow in the sump. Minimum level of air-water interface and iso-surfaces of vortices were used to identify the location and shape of the free surface as well as surface vortices. By monitoring the air-water interface with varying flow rate, it was found that when the flow rate increased, more free surface vortices appeared. The formation mechanism of free surface vortices and the pulling air bubbles as well as the development process of vortices were clarified by using the volume rendering method and air volume fraction contours. The locations of the center core of air-entrained vortices on the free surface were in good agreement with those of experiments. Detailed investigation of surface vortex behavior with respect to flow rates were made and discussed.

numerical analysis, VOF multiphase model, free surface vortex, vortex behavior, minimum level of air-water interface, pump sump.