Double Overhung Disk and Parameter Effect on Rotordynamic Synchronous Instability—Morton Effect—Part II: Occurrence and Prevention

Abstract

This paper performs the parametric studies corresponding with the theoretical Morton effect (ME) model explained in Part I of this paper, where the fully nonlinear transient analysis based on the finite element method is introduced. Operating parameters, such as oil supply temperature, bearing clearance, oil viscosity, etc., are perturbed from the testing conditions to investigate the shifting of critical speeds and ME instability onset speed (IOS). The ME is significantly affected by the rotor bending mode with large overhung deflections, and operating parameters should be adjusted to increase the separation margin between the operating speed and the corresponding critical speed for ME mitigation. Reducing the carryover flow ratio and using the asymmetric bearing pivot offset are capable to suppress the ME by reducing both the average and differential journal temperature. The heat barrier sleeve with air or ceramic isolation is designed to prevent the heat flux into the journal and can successfully mitigate the ME based on the simulations.