An Experimental Study of High-Speed Rotors Supported by Air-Lubricated Foil Bearings—Part 2: Response to Impact and to Periodic Excitation

Abstract

A high-speed rotor, supported by an air-lubricated foil bearing is stable at speeds up to and in excess of 60,000 rpm. “Natural frequencies” are determined at various rotational speeds from records of response following impact of the rotor housing. The foil-rotor system is subjected to periodic, unidirectional excitation by means of a vibrator (shake table) and the in-line and transverse responses are obtained in a frequency range 50–2000 cps. The behavior of the system is similar to that of a simple, damped oscillator, characterized by a single resonance in the low-frequency range. Experimentally determined values of resonant frequencies are in fairly good agreement with predicted results, based on a simplified theoretical formulation of the problem. Responses of rotors to (a) excitation of variable amplitude at resonance and to (b) excitation of variable amplitude at frequency equal to half the rotational speed are investigated. It is found that excitation and rotor excursion are nearly colinear, except in the neighborhood of resonance. Excitation at frequency equal to half the speed of rotation is not associated with large amplitudes of motion, wherein the foil bearing compares favorably with other types of fluid-film bearings.