Air-core vortex usually occurs at hydraulic intakes. It degrades the hydraulic performance and causes vibrations of the pump or turbine, resulting in a decrease of the efficiency and safe stability of hydraulic engineering. In this paper, large eddy simulation using an in-house code is performed for a two-phase incompressible fluids flow to investigate the air-core vortex phenomenon. The air-water interface is captured by the coupled level-set and volume-of-fluid (CLSVOF) method. The CLSVOF method takes advantages from the level-set method and the volume-of-fluid method, and improves accuracy of interface reconstruction and mass conservation property. A pump suction model based on a submerged sink and an intake flow field of the pumping station based on a pair of sink and source were set up for the numerical simulation of the air-core vortex phenomenon, which simplified the mechanical structure of the pump, and the flow characteristics of the intake flow induced by the pump suction were well embodied. The air-core vortex phenomenon was well reproduced in the simulation, and the evolution process from surface swirls to a fully-developed air-core vortex during its formation was presented. Analyses of the Reynolds stress during the air-core vortex formation elucidates motions of vortical structures and momentum transmission between the dominant vortex core of the air-core vortex and its ambient vortices, which reveals the development characteristics of anisotropic turbulent structures during the air-core vortex formation and further deepens the understanding of mechanisms underlying its formation. At the surface swirl stage of the air-core vortex, it can be seen from the distribution of Reynolds stress along the streamwise and spanwise directions that there is a peak of the Reynolds normal stress at the intake along the streamwise direction, and the Reynolds normal stress of the left and right sides of the intake are monotonically increased or decreased, respectively. The crests and troughs of profiles of the Reynolds normal stress along the spanwise direction appear alternatively, which indicates that vortices of the two sides of the intake move towards the intake and randomly gather at the near free-surface region above the intake. At this stage, the streamwise component of the Reynolds normal stress is dominant. The intensity of turbulence increases with time. There are two crests of profiles of the Reynolds normal stress along the streamwise and soanwise directions, which indicates that there are two strong vortices in the near region of the intake. The distribution of the Reynolds shear stress manifests that the random vortices evolve into two strong vortices by momentum transmission among vortices. The spanwise component of the Reynolds normal stress is dominant at this stage. Two strong vortices further evolve into a dominant vortex, and its intensity increases with time and draws air into the intake, forming a visible fully-developed air core whose tip reaches to the intake.


Les Study of the Reynolds Stress During the Formation of the Air-Core Vortex in Hydraulic Intakes

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2020/volume/83709

18th International Conference on Nanochannels, Microchannels, and Minichannels
Paper Proceedings: https://asmedigitalcollection.asme.org/ICNMM/ICNMM2020/volume/83693

Fluids Engineering Division Summer Meeting
Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2020/volume/83716

HT-ICNMM2020 - Virtual Conference, SHTC - Virtual Conference, FEDSM2020 - Virtual Conference

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