Analysis On Dynamic Characteristics Of Multistage Centrifugal Pump Rotor

The rotor of a centrifugal pump is the core component of a multistage centrifugal pump,and its stability directly affects the normal operation of the multistage centrifugal pump.Due to the strong vibration generated when the rotor reaches the critical speed,which affects the stability of the rotor operation,it is necessary to analysis the vibration characteristics of the rotor deeply.In order to achieve technological improvement and efficiency,centrifugal pumps are developing towards high power and high efficiency.It is necessary to conduct in-depth research on the dynamic characteristics of centrifugal pumps.Therefore,the dynamic characteristics of the single stage centrifugal pump rotor were analyzed in this study firstly.Then,the three-dimensional dynamic analysis model of the multistage centrifugal pump rotor was established to study the dynamic characteristics of the multistage centrifugal pump rotor.The dynamic characteristics of centrifugal pump rotors with typical cracks have been discussed,which will provide support for the overall design and fault diagnosis of multistage centrifugal pumps,and have outstanding practical engineering significance.Firstly,a three-dimensional dynamic analysis model of the rotor of a single stage centrifugal pump is established in this thesis.The vibration mode and critical speed of the rotor of a single stage centrifugal pump were studied using finite element method,and the dynamic deformation distribution of the single stage rotor was analyzed and discussed.Furthermore,the gyroscopic effect was taken into account in this study,and the modal calculation formula for a single stage centrifugal pump rotor containing the gyroscopic effect was obtained.The study showed that the gyroscopic effect can promote the forward vortex of the centrifugal pump rotor while suppressing its reverse vortex.The Riccati transfer matrix method was used to calculate the first and second critical speeds of a single stage centrifugal pump rotor,and the results were compared with the finite element analysis results to verify the correctness of the calculation and analysis method for the critical speed of a centrifugal pump rotor in this thesis.Secondly,based on the analysis of the rotor dynamics model of a single stage centrifugal pump,the axial force and bearing support stiffness of the multistage centrifugal pump are considered in the analysis model of a certain type of multistage centrifugal pump in Chongqing Water Pump Factory.And a more complex multistage centrifugal pump rotor dynamics analysis model is established.The critical speed of a multistage centrifugal pump system is calculated and analyzed.By comparing and analyzing the results with experimental measurements,the correctness of the finite element analysis model was verified.The research results indicate that the influence of axial force on the vibration mode and natural frequency of the multistage centrifugal pump rotor is not significant.However,as the bearing support stiffness increases,the natural frequency of the multistage centrifugal pump also increases.When the bearing support stiffness reaches a certain value,the natural frequency of the multistage centrifugal pump rotor subsystem remains unchanged.Then,the impact of unbalanced mass on the centrifugal pump is further considered.By calculating and analyzing the vibration response characteristics of multistage centrifugal pumps,the influence characteristics of unbalanced mass on the steady-state and transient responses of the rotor system of multistage centrifugal pumps are analyzed and discussed.The research results indicate that the vibration amplitude at the middle position of the multistage centrifugal pump rotor is higher than that at both ends of the rotor.As the unbalanced mass increases,the steady-state response peak at different positions of the multistage centrifugal pump rotor will also increase.The transient analysis of the corresponding multistage centrifugal pump rotor shows that the rotor of the multistage centrifugal pump is in the most unstable state during the startup process and the shaft centerline orbit is spiral.Further considering the unbalanced mass during the startup process of the multistage centrifugal pump rotor,it can be found that the unbalanced mass will cause an increase in the vibration amplitude of the multistage centrifugal pump rotor,and the corresponding shaft centerline orbit will also be more unstable.Finally,the working environment of rotor fatigue can easily lead to the initiation and propagation of structural cracks,which has a significant impact on the normal maintenance of multistage centrifugal pumps.A dynamic analysis model for the rotor of a multistage centrifugal pump with cracks has been established.The calculation results show that the shaft centerline orbit of the rotor of the multistage centrifugal pump with cracks presents an "inner eight" shape,and the vibration of the rotor of the multistage centrifugal pump becomes more intense as the crack position is closer to the middle of the rotor.Furthermore,by establishing a crack stress intensity factor analysis model for the rotor of a multistage centrifugal pump,the stress intensity factors of elliptical cracks at different positions of the rotor were analyzed.On this basis,the crack propagation of the multistage rotor of a centrifugal pump under periodic load was calculated.The research results showed that as the number of load cycles increased,the depth of crack propagation gradually increased and the propagation rate also increased.