An experimental determination of the instability of a flexible rotor in four-lobe bearings

Abstract

A pair of preloaded four-lobe bearings were experimentally tested with a simple flexible rotor and the unbalance response and instability threshold were determined. Ten orientations of the bearings were used. Before each test the bearings were repositioned circumferentially. Measurements included total response, synchronous response and frequency spectra at various running speeds. The rotor—bearing system exhibited the highest and lowest instability threshold for approximately load-off-pad and load-on-pad operating conditions respectively. The critical speed of the rotor system was 3000 rev min −1 and oil whip occurred at speeds of 6600 rev min −1 to more than 12500 rev min −1 depending on bearing orientation. The results showed moderate agreement with theoretical predictions.