Suction Vortices in a Pump Sump—Their Origin, Formation, and Dynamics

Abstract

The origin, formation mechanism, and dynamics of suction vortices in a pump sump have been clarified by large eddy simulation (LES) applied to two different computational models. The first one is a pump-sump model with uniform flow entering a water channel of rectangular cross section and a vertical suction (outlet) pipe installed at its downstream end. LES with different wall boundary conditions have revealed that the origin of a submerged vortex is the mean shear of the approaching boundary layers that develop on the bottom and side walls of the sump. Detailed investigations have revealed that deviation of the mean flow triggers conversion of the vorticity axis to the vertical direction. The local acceleration of the vertical flow stretches the aforementioned vertical vortex, which results in the formation of a submerged vortex. The second one is a simplified computational model composed of a paraboloid of revolution and aims to accurately simulate the stretch of the viscous core of a submerged vortex that has appeared under the suction pipe of the pump-sump model. The differences between the models, especially predictions of the minimum pressure, imply that cavitation could have been initiated in the viscous core, if it had been taken into account, as is observed in the pump-sump experiment at the same condition. Parametric studies with different initial swirl numbers from 0.12 to 16.3 have clarified the behavior of the submerged vortex. It was found that a strong submerged vortex appears only at a relatively small range of the swirl numbers from 1.25 to 3.

Study on the Vortex in a Pump Sump and Its Influence on the Pump Unit

“…The VOF model is a surface tracking method, which is suitable for a continuous two-phase flow with obvious interface. The mixture model is suitable for the flow where each phase is treated as a continuum connected to each other in the Euler model, which is realized by solving the momentum equation of the mixture and that is mainly applied to the calculation of particle flow and sedimentation [27]. The Euler model is mainly used for bubble flow, particle suspension and sedimentation, by solving the multiple momentum equations and continuity equations [28].…”

Formation Mechanism of an Adherent Vortex in the Side Pump Sump of a Pumping Station

“…The 3D unsteady turbulent flow in the sump has been simulated with four different turbulence models, namely, standard k-ε, realizable k-ε, renormalization group k-ε, and shear stress transfer k-ε volume of fluid (VOF) multiphase models [9]. The causes and influencing factors of the inspiratory vortex in the sump have also been analysed with large eddy simulation (LES) technology [10]. In these previous studies, numerical simulation was used for a detailed analysis, but no physical model was adopted to verify the results, leading to the lack of credibility.…”