Investigation on the air-core vortex in a vertical hydraulic intake system

Abstract

Air-core vortex occurred at the hydraulic intakes deteriorates the performance and operation stability of hydraulic machineries. To investigate the evolution process and generation mechanism of the air-core vortex formed at the vertical intake, large-eddy simulation with the coupled level-set and volume-of-fluid method is performed in a pump sump. This paper elucidates the evolution of velocity distribution caused by pump suction, and associations between vortices motions and velocity evolution and the accompanying free-surface deformations are clarified, which reveals the generation mechanism and evolution characteristics of air-core vortex. Vortices are created by the disturbances of small recirculation zone around the intake pipe. The recirculation is caused by the interaction of the wall of vertical pipe and converging flows with opposite directions driven by the pump suction. The enhancement of vortices due to vortex distortion dominates the air-core vortex formation, and the vertical stretching effect accounts for about 70%. The meandering characteristics of air-core vortex are characterized through analyses of meandering scope and velocity distribution, and the convection of mean flow and sump wall take the leading role in causing its meandering.