Under normal operation, a rotor levitated by magnetic bearings will rotate without making contact with any stator component. However, there are a number of circumstances that may lead to temporary or permanent loss of levitation. These include full rotor drop events arising from power loss, momentary fault conditions, sudden changes in unbalance, high levels of base acceleration, and other aerodynamically induced force inputs. The spinning rotor will come into dynamic contact with an auxiliary bearing. Highly localized and transient temperatures will arise from frictional heating over the dynamically varying contact area. Rotor dynamic contact forces are predicted for a range of initial conditions leading to combinations of bounce and rub motion on the auxiliary bearing. The transient heat flux from the contact area is then ascertained. A transient thermal Green’s function is developed in a form that is effective over short or long time scales and local to the source. This enables the transient thermal response of an auxiliary bearing to be assessed for a range of dynamic contact conditions. Auxiliary bearings consisting of fixed bushings and free to rotate inner races are analyzed. The results show that significant localized contact temperatures may arise from each contact event, which would accumulate for multiple contact cases. The methodology will be of relevance for the life prediction of auxiliary bearing designs.

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Annular components are used widely in engineering systems and include bearing bushes and races, which may be exposed to extreme operating conditions. A method to establish the localized transient thermoelastic deformation of a homogeneous two-dimensional annular component is developed. The analysis is based on solving the thermoelasticity equations using a state space formulation for the Fourier components of the radial and tangential displacements. Two boundary conditions are considered, namely, rigid and resiliently mounted outer boundaries, both associated with stress free inner boundary conditions. The thermoelastic solution is then demonstrated for a transient temperature distribution induced by inner boundary frictional heating due to rotor contact, which is derived from a dynamic Hertzian pressure distribution. The application is to a relatively short auxiliary bearing for which a state of plane stress is appropriate. However, the thermoelastic analysis is generalized to cover cases of plane strain and plane stress.

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.

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