Levitation characteristics of a squeeze-film air journal bearing at its normal modes

Abstract

A tubular squeeze-film journal bearing was designed such that it flexed its shell at its normal modes producing a triangular modal shape. The shell motion was created by a single-layer piezoelectric actuator powered at 75 V AC with a 75 V DC offset and the driving frequency coincided with the modal frequency of the bearing. The paper provided a theory that shows the existence of a positive pressure in a squeeze film responsible for the levitation phenomenon. The various modes of vibration of the tubular bearing, made from AL2024-T3, were obtained from a finite element model implemented in ANSYS. Two normal modes, the 13th and 23rd, at the respective theoretical frequencies of 16.37 and 25.64 kHz, were identified for further investigation by experiments with respect to the squeeze-film thickness and its load-carrying capacity. While the bearing at both modes could cause levitation, the 13th mode has a greater load-carrying capacity because its modal shape produced a much lower end leakage.