Abstract
Free surface vortex (FSV) is a complex gas-liquid two-phase flow, which is harmful to the pump unit. In this paper, FSV in the pump sump with a double-suction centrifugal pump is numerically simulated by two-phase flow method, which is verified by experimental data and agreed well with theoretical models. The purpose of this paper is to study the influence of FSV on the performance of pump, the variation characteristics of several paramount paraments (FSV evolution process, vortex strength, air-laden content, head-drop, flow stability, pressure amplitude) was revealed for the first time. The vortex strength affects the air-laden capacity of FSV, the maximum air content in this impeller can reaches 17.1%. The air destroys the stable structure of the flow field in the impeller, affects the flow rate, and the mean head-drop by 36.8%, meanwhile inducing irregular pressure pulsation. The duration and content of suction air of FSV determine the performance-drop amplitude. The change of unit performance is proportional with the air-entrainment content and vortex strength, which shows that the larger the FSV air-entrainment is, the worse the pump performance. It is clear that the predicted results are consistent with the existing problems of the unit on site, which can provide a method to predict the influence of the FSV on the unit.
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