An Investigation into the Physics Behind the Stabilizing Effects of Two-Phase Lubricants in Journal Bearings

Abstract

Solid phase particles in two-phase lubricants used in journal bearings undergo deformation in the bearing clearance space during large amplitude journal whirl. The orbital energy causing instability of the rotor shaft is drawn from the drive and it is proportional to the orbital area whereas energy dissipation offered by the fluid film is a path function. The balance of these two energies decides the stability of rotor-bearing system. In the first part of this paper, equivalent snubber springs have been used to represent contact with solid phase particles and purely elastic collision is modeled. It is analytically shown that any perturbation of a circular orbit increases dissipative work, which may entrain the response of an otherwise unstable system (i.e., without perturbation) to a stable orbit. In the second part of this paper, a rigid rotor supported on journal bearings using two-phase lubricants is studied and it is shown that discontinuity in the support forces arising out of contact with solid-phase particles, irrespective of the nature of deformation of particles, is responsible for controlling the whirl orbit size.