Thermoelastic growth of an auxiliary bearing surface due to repeated rotor dynamic contact and rubbing

There are a number of important issues relating to rotor/auxiliary contact in magnetic bearing systems. Primarily, an auxiliary bearing must prevent rotor/stator contact during events such as system power failure and large scale input disturbances. The auxiliary bearing may experience repeated contacts ranging from short timescale transient events to longer timescale rubs. While many studies of the rotor dynamic responses have been undertaken and reported in the open literature, the associated problems relating to thermoelastic distortion have received relatively little attention. These are important since high initial slip speeds will lead to localized heating that may cause large and highly transient surface temperature changes. Repeated contact events or repeated rubbing over a surface deformation may also lead to an accumulative increase in the level of surface distortion. This paper presents a study of the methodology that could be used to assess the overall thermoelastic distortion between a rotor and an auxiliary bearing. It shows that an assessment of the dynamic accumulation of distortion is possible from fundamental studies of individual contact events. The results from case studies highlight the possible problems that could be caused by clearance reductions during operation.