Experiments and Stability Predictions of Two Sets of Tilting Pad Bearings on an Overhung Rotor

Abstract

An overhung rotor was experimentally tested in two sets of five shoe tilting pad bearings. The preload factors of the two sets were 0.1 and 0.5, respectively. The rotor had critical speeds at 3000 and 6800 rpm. When mounted on the first set of bearings, the rotor remained stable for speeds over 11 000 rpm. However, when mounted in the second set of bearings the system went unstable due to whip at 10 400 rpm. A theoretical analysis was performed on the stability of the rotor system to determine if the bearings were the cause of the whip. The analysis indicates that the system is marginally stable, and that small cross couplings generated by the disk-shaft mountings destabilized the system. Also, pad inertia has little affect on the stability of this particular rotor. The system was predicted to be the most stable when mounted on the bearings with a preload of 0.1, so that the predicted trends with varying preload were correct. The predictions also indicate that subsynchronously reduced bearing coefficients...