The Synchronous Rotor Instability Phenomenon (Morton Effect)

Abstract

This paper gives an overview on the "Morton Effect" and explains how synchronous rotor instability, due to nonuniform heating of bearing journals, can occur in high-speed turbomachinery. Theoretical investigation by Keogh and Morton (1993, 1994) indicate that rotors supported by fluid-film bearings inherently exhibit a nonuniform temperature distribution along the bearing journal circumference. This thermal effect results in rotor bending which can, in combination with an overhung mass such as couplings and overhung impellers, significantly increase rotor unbalance and thus synchronous rotor vibration. Under certain condition, it can lead to synchronous rotor instability. Experimental studies have subsequently been performed verifying the existence of this rotordynamic phenomenon (de Jongh and Morton, 1994) that is more commonly known as the Morton Effect. In this paper, the phenomenon is explained and an overview is given of the existing literature on this subject. A number of technical papers show pragmatic solutions for unstable synchronous rotor behavior. These are discussed in more detail.