Numerical simulation of freesurface vortex and theoretical analysis on vortex/sink model
YANG Fan, SHI Xu-Ming, DAI Ren, GUO Xue-Yan, CHEN Tie-Jun, WU Yu-Lin
(1. School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China; 2. State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, China)
Abstract：To study the formulation mechanism of suction vortex and put forward some related theoretical analysis, the phenomenon of freesurface vortex often observed above a drainage intake was simplified into a model of discharging sink water, which was simulated by using VOF (volume of fluid) method and RNG k-ε turbulent model. The process of suction vortex evolving from freesurface vortex was numerically simulated. By comparing the calculated results with Burgers vortex theory, it is found that the tangential velocity distribution equation in Burgers vortex model agrees with the calculation; and that vortexes gather towards the center is one of the factors that cause the freesurface to depress and eventually become suction vortex. It is also found that the other two velocity distributions in Burgers vortex model, the radial and axial velocity distribution equations, in comparison with the calculation, were theoretically incorrect. To further simplify the model, ruling out tangential velocity, water discharge without vortex was simulated. To clarify the sink effect for surface depression, through theoretical deduction, based on spherical coordinate system, a kind of spherical sink model was proposed, with which a better velocity distribution equation was obtained. “Sink” effect is one of the important factors that lead to suction vortex phenomenon.
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