Abstract: Similar to the principle of desilting funnel, vortex basin for oncemelania separates oncemelania from water by spiral flow. A full understanding of the flow field in the vortex basin is essential to investigating into the separation mechanism. In this paper, the Reynolds Stress Model and VOF method are applied to simulate water-air two-phase flow in vortex basin. The calculated results of free surface and three-dimensional velocity are in good agreement with experimental data. The simulation results show that tangential velocity reduces with the decrease of distance from the center of the basin, resembling the velocity distribution of forced vortex. Analysis on the distribution of secondary flow indicates that deflector plays a key role in the efficient removal of oncemelania by suppressing the upwelling current on the sidewall and weakening the secondary flow carrying oncemelania.The research result offers technical support for controlling oncemelania and improving vortex basins.

Key words: vortex basin for oncemelania, numerical simulation, flow characteristics, secondary flow, deflector