Air-core vortex often appears at the hydraulic intakes, it not only degrades hydraulic performance but also causes vibrations of the pump or turbine, resulting in efficiency reduction and operation instability. In this paper, large eddy simulation using an in-house code with the coupled level-set and volume-of-fluid method for capturing the air-water interface is performed. Vortices motions and turbulent characteristics are investigated. The fully-developed air-core vortex is well reproduced in the simulation. The distribution of the turbulent kinetic energy of the flow field is relevant to the evolution of vortices during the air-core vortex formation. At the early stage of the air-core vortex formation, the turbulent kinetic energy is high near the intake and the two side of the intake along the streamwise direction, and the streamwise component of the Reynolds normal stress is dominant, which indicates that vortices on the two sides move towards the intake along the streamwise direction and gather near intake. The turbulent kinetic energy increases rapidly as it approaches to the intake, and it has two peaks near the intake with the development of the flow field, which indicates that the gathered vortices evolve into two strong vortices. The turbulent kinetic energy only has one peak at the late stage, which indicates that there only exists one dominant vortex, and air is entrained in the intake, forming a fully-connected air-core vortex.

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