Evolution of air-entraining vortices in inclined intake pumping stations under low sump water depth condition

The air-entraining vortices may appear in a pump sump when the pumping station operates at a low water depth, which will induce undesirable phenomena such as cavitation and vibration. In this paper, the evolution process of air-entraining vortices is studied in detail based on the volume of fluid (VOF) two-phase flow numerical simulation method, to clarify its hydraulic characteristics and influence. The results show that the water-air interface in the sump varying periodically with time under a low water depth consists of four stages, that is, slow rise, fast rise, continuous stability and reduction. The shape of the air-entraining vortices shows a periodic evolution under the interference of water surface fluctuations, from the surface dimple to the full air core to intake, then to the vortex pulling air bubbles to intake, and finally back to the surface dimple. The inhaled air volume fraction in the suction pipe changes with the evolution of the air-entraining vortices. In addition, the average angle of velocity distribution and the average swirl angle are analyzed in depth to improve the understanding of flow pattern caused by the complicated and diversified inhaled air.