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| Analysis of inner flow in low-specific centrifugal pump at conditions near hump |
| Mao Jieyun, Yuan Shouqi, Zhang Jinfeng, Li Yalin, Wang Yefang |
| National Research Center of Pumps, Jiangsu University, Zhenjiang, Jiangsu 212013, China |
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Abstract To investigate the mechanism of hump, the inner flow characteristics of a low-specific pump around hump condition were analyzed using CFD simulation method and the relationship between head and inner flow distribution was established. The relative error was below 3.62% at 0.1~0.6 times of the designed flow rate. The flow rate from the simulation that the hump occurred agreed with the test very well. Analyzing the inner flow at 0.2, 0.3 and 0.4 times of the designed flow rate, results show that a large amount of back-flow could be found in the inlet channel and caused the pre-swirl before the pump inlet which induced hump further. The vortices appeared in all impeller passages of all kinds of sides. At 0.2 and 0.3 times of the designed flow rate, the vortices even choked the passages, disturbing the normal flow. The relative velocity was large at outlet of the passages with vortices, while the absolute velocity was very small. It caused the decrease of the head and even the hump when analyzing from the pump basic equation. When comparing the impeller outlet absolute velocity at R/R2=0.9 with other flow rates, it could be found that at these three flow rates the velocity fluctuated more and the circumferential component decreased more obviously, inducing the decrease of head. The pre-swirl at impeller inlet and the back-flow at impeller outlet are the reasons of hump, so eliminating or restraining these unsteady phenomenon could be the starting points of restraining the hump.
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Received: 26 July 2014
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