The Dynamic Characteristics of a Turborotor Simulator Supported on Gas-Lubricated Foil Bearings—Part 1: Response to Rotating Imbalance and Unidirectional Excitation

Abstract

A 16-in-long rotor, weighing approximately 21 lb, was supported by air-lubricated foil bearings. In physical size and in mass distribution, the rotor was closely matched with that of an experimental Brayton cycle turboalternator unit. The rotor was stable in both the vertical and horizontal attitudes at speeds up to 50,000 rpm. A detailed description of the experimental apparatus and of the foil bearing design are given. The paper contains data of response of the rotor to rotating imbalance, symmetric and asymmetric, and to excitation by means of a vibrator (shake table). It is concluded that the gas-lubricated foil-bearing suspension is free from fractional-frequency whirl and suffers no loss of load capacity when excited at frequency equal half the rotational speed. On contrast with rigid gas bearings, the foil bearing imposes no stringent requirements with respect to dimensional tolerances, cleanliness, or limitations of journal motion within the narrow confines of bearing clearance.