Journal bearing differential heating evaluation with influence on rotor dynamic behaviour

The nature of differential heating across the journal of a hydrodynamically lubricated bearing has been investigated theoretically and an assessment made of the local thermal bend in the rotor at the bearing location. The energy balance for the system is time dependent and involves a stationary bearing component, an oscillating lubricant film, and a rotating, orbiting section of journal. Thermohydrodynamic solutions are developed which allow for temporal and spatial periodic variations of bearing, lubricant and journal temperatures. The influence of a synchronous journal orbit on the temperature distribution throughout the system is discussed. In particular, the relation between any prescribed orbit and the steady state temperature differential across the journal, resulting in steady state rotor bending, is established. The role played by such thermal bending in the onset of unstable synchronous whirl in the rotors of high-speed machines is outlined.