Abstract In order to improve the critical speed of multistage centrifugal pump rotor system effectively, the effects of several impact factors on the speed or natural frequency of the rotor are analyzed and compared by means of rotor dynamics and finite element method. Additionally, the vibration modal analysis is conducted based on a whole rotor system, and the corresponding bending and torsional vibration modal shapes are provided as well. A quantitative comparison of the fluid-structure interaction and spin softening effect on natural frequency or critical speed is made, the factors affecting the critical speed of rotor and the optimization methods for the speed are given, and the numerical analysis and experimental results are compared. It is shown that accurately simplifying support, reasonably determining support stiffness and damping matrix are necessary prerequisites for precise predictions of critical speed. The fluid-structure coupling effect is equivalent to add a virtual mass on the rotor. The spin softening effect works by the Coriolis effect. The "dry" and "wet" critical speeds of multistage centrifugal pump rotor are quite different. The calculated and measured critical speeds are in good agreement. The numerical simulation of ANSYS is in a good accuracy and can provide a certain reference for the rotor design of multistage centrifugal pump.
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