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| Numerical simulation of axial pump unit startup process using VOF model |
| ZHOU Daqing, LIU Yuefei |
| College of Energy and Electrical Engineering, Hohai University, Nanjing, Jiangsu 211100, China |
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Abstract To reveal the start-up transient laws of the external parameters and the flow pattern in the passage of the axial pump unit, three-dimensional numerical simulations have been conducted on the geometrical model of the whole flow system including the inlet conduit, runner, stay vanes, siphon outlet passage and upstream reservoir under the two conditions: preopening vacuum breaker valve and maintaining the valve close. The volume of fluid(VOF)model was adopted and the Realizable k-ε turbulence model was applied to close the governing equations. Numerical results showed that when the water flow went over the hump, the air within the outlet passage continuously was involved into the water and discharged by the vortex in the declining section of the outlet passage so that siphon formed eventually. The larger the original bubbles in the outlet passage were, the longer the time of syphon formation required. Compared with the scheme of keeping the vacuum breaker valve closed, opening the vacuum breaker valve in advance can make the maximum pump lift decrease by 30% and the start-up time shortened by 64%.
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Received: 10 June 2016
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