Rotor-Bearing Stability

Abstract

This paper presents a survey of the various mechanisms that can cause instability in rotor bearing systems. The occurrence of self-excited instability is of particular importance to the manufacturers and users of modern turbomachinery particularly with the present trends to· wards high speed and loading conditions. The paper presents stability data on plain and multilobed journal bearings and shows the effect of unbalance and external loading on the nonlinear rotor whirl orbits. In addition to the stability characteristics of hydro· dynamic bearings, instability due to internal friction, aerodynamic cross coupling and seals is also discussed. The paper discusses how many of these instabilities may be avoided by proper bearing and support design. In addition to the theoretical prediction of rotor whirl orbits, actual case histories of rotor instability are presented.