A numerical study on the behavior of surface vortices in a pump suction sump was performed. A finite volume method with a RANS turbulence model and a VOF multiphase model was applied to solve the sump flow with a single intake channel. Multi-blocked structured grids and the open channel model were used to capture the flow behavior and their mutual interactions between air and water phases with higher accuracy. Air-water interface level, air-entrained vortex length, and air volume fraction contours and iso-surfaces were used to visually identify the location and shape of the free surface as well as surface vortices. By monitoring the vortex length with varying water level, it was found that lower water levels induced stronger free surface vortices. The behavior of surface vortices and air bubbles caused by breaking off air-entrained vortices was explained well by using the volume rendering method and air volume fraction contours. The predicted velocity distributions at the entrance of bell mouth were in a good agreement with those of experiments.

numerical analysis, VOF multiphase model, free surface vortex, vortex length, pump sump.