Calibrating a Large Compressor's Rotordynamic Model: Method and Application

This paper defines and demonstrates an effective, sequential process of rotor bearing model calibration, for a large centrifugal compressor. The calibration process involves a series of measurements and corresponding predictions, including free-free mode shapes and frequencies, casing shaker test data, amplitude and phase variation with speed, and change of vibration with known changes in unbalance. The process first uses the measured free-free data and comparison with matching predictions to calibrate the mass elastic model for the rotor alone; it then applies measured casing response to shaker excitation, measured variation of frequency and phase, and dual peak characteristics at the first critical speed, to identify the correct support characteristics. The paper demonstrates application of the calibrated model and established uncertainty in its predictions to assure integrity not readily demonstrated by testing alone. Specifically the margin between maximum continuous speed and the second critical speed is shown to be acceptable, and the amplitude of vibration at maximum continuous speed is shown to stay well below the seal clearances at all seal locations.