Modal analysis of super low-specific-speed self-balancing multistage centrifugal pump rotor
YANG Yongfei1, LI Wei1*, SHI Weidong2, MA Xinhua1, ZHANG Wenquan1, XU Rongjun3
1. National Research Center of Pumps, Jiangsu University, Zhenjiang, Jiangsu 212013, China; 2. School of Mechanical Engineering, Nantong University, Nantong, Jiangsu 226019, China; 3. Lanshen Group Limited by Share Ltd., Nanjing, Jiangsu 211500, China
Abstract To grasp vibration characteristics of multi-stage centrifugal pump rotor and avoid occurrence of resonance during pump operation so as to guarantee the stability of operation, modal analysis on the rotor of a super low-specific-speed and self-balancing multistage centrifugal pump was carried out based on the commercial software ANSYS Workbench in this article. Natural frequencies under three conditions namely dry rotor without flow field pre-stress, dry rotor with flow field pre-stress and wet rotor with flow field pre-stress were calculated and compared. Further, the first eight modals of the rotor were extracted and analyzed. It is shown that the natural frequency of reverse precession is lower than that of forward precession for the same order. The natural frequency increases slightly under condition with flow field pre-stress compared with that without pre-stress, indicating that the flow field pre-stress can rigidize the pump rotor in a certain degree. Under wet condition, additional mass, viscous and damping effects of water have intensively decreased influence on the natural frequency, and the mass force of water has a more significant effect on the frequency. By comparing the first four order vibration modes of the pump rotor, it is found that vibration mode and position where the maximum vibration amplitude appears are identical basically under three conditions. The third order vibration is rotational vibration around the pump shaft-axis, while the other three vibrations correspond to bending vibrations with di-fferent directions and shapes.
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