A Thermoelastohydrodynamic Model of The Morton Effect Operating in Overhung Rotors Supported by Plain or Tilting Pad Journal Bearings

Abstract

Unlike most instabilities, which are non-synchronous in nature, the Morton Effect is a synchronous phenomenon. This thermal instability occurs primarily in overhung rotors that are supported by fluid film bearings and is caused by differential viscous shearing within the bearing lubricant. The Morton Effect has also gained much attention within the last decade. Prior studies of the Morton Effect have used complex analysis in the frequency domain to model this instability. However, such an approach makes it difficult to develop a user-friendly design tool for engineers. The current research employs a steady-state analysis to predict the onset of the Morton Effect, and it uses an instability criterion which is based on a threshold unbalance caused by a force equal to 15% of the weight of the rotor. It is hoped that this method will provide a more easily adaptable platform for design and analytical purposes. The current model has demonstrated good agreement with other theoretical models and experimental data. This agreement applies to rotors that are supported by either plain or tilting pad journal bearings and it was found that a worse case scenario for the Morton Effect would involve centered, circular and large-amplitude bearing orbits. A test rotor was also designed and built. Initial experimental data revealed an unusual instability that might have been caused by the Morton Effect.