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Rotor Dynamics Analysis of a Multistage Centrifugal Pump

Harisha.S, Dr. Y.J. Suresh

A rotor dynamic model is developed by using finite element method (FEM), The rotor includes impellers, bearings and seals.The object of the analysis is to calculate the critical speeds of a rotor to find out if there are sufficient margins of separation between critical speed and the rotor operating speed. Lateral resonant frequencies can excite on the rotor and result in high damaging rotor vibration. The torsional critical speed of rotating machinery components is an important consideration in defining the operational reliability of the rotary equipment train. Pump is mainly a 4 staged centrifugal pump, the modal analysis of the centrifugal pump is performed using ANSYS workbench is used as a FEA tool to find critical speeds or rotor natural frequencies. To meet the higher target of power, machines have to run at higher speeds then pump shaft will be subjected to higher lateral and torsional vibrations because of gyroscopic effect and centrifugal force of the rotating elements mounted on the shaft. The resonance is produced when the rotor natural frequency coincides with operating frequency, the deflection of the rotor will be maximum. To avoid resonance condition, it is necessary to evaluate all stiffness and damping coefficients of wear rings, mechanical seals, throttle seals and bearings. In this work an attempt is made to evaluate the Lateral critical speeds using ANSYS software by plotting Campbell diagrams and is compared with theoretical calculations and RBTS (Rotor Bearing Testing Software). It is very difficult to eliminate all interference points in the system since there are so many external excitations. The rotor has been designed and analyzed by using the guidelines as per API 610 standards.