A New Computer Program For Pump Rotordynamic Analysis

Abstract

A new computer program for pump rotor analysis has been developed to improve the accuracy of critical speed, stability, and response calculations for multistaging centrifugal pumps. The program capabilities include: (1) two nonlinear journal bearings, each with eight speed-dependent stiffness and damping coefficients and with flexible bearing supports, and, (2) up to seventeen seal stations with radial and angular seal misalignments and with each seal or impeller represented by full 4 x 4 speed-dependent stiffness, damping and inertia matrices. Also, speed-dependent steady-state impeller fluid forces are accounted for. The program has the additional capability to automatically account for the nonlinear variation of the bearing coefficients resulting from part of the rotor weight being supported by the seals. This is believed to be the most advanced computer program currently available for pump rotor analysis. At the same time, the implementation is user friendly and can be run with different levels of sophistication, depending on user needs and available input data. The program has been used to analyze a multistage centrifugal pump for which a natural frequency had been measured during normal operation. Both the addition of inertia coefficients to the seal model and the extension of the seal model to include moment coefficients had significant effects on rotordynamics. The natural frequency prediction, for example, improved significantly. The improved bearing coefficients, however, had little influence on the particular pump rotor analyzed.