Theoretical analysis on the static and dynamic performances of a squeeze film air journal bearing with three separate pads structure

Owing to their distinct non-contact and oil-free characteristics, squeeze film air bearings have been introduced to satisfy ultra-precision, low wear, and ultra-clean requirements. This paper proposes an analytical model of a three-pad squeeze film bearing to study its static and dynamic performance. The bearing force is calculated by integrating the pressure distribution over the bearing surface, which is governed by the Reynolds equation. The stable equilibrium position of the rotor is obtained by the Newton-Raphson method. A numerical method to acquire the bearing dynamic coefficients is originally proposed by considering the vibration of its pad. These dynamic coefficients are determined by solving the perturbation equations derived from the combination of the Reynolds equation and the modified film thickness and pressure. The predicted static and dynamic results show good agreement with experimental results. The parameter study shows that the variation in eccentricity with respect to the rotational speed can be controlled by reasonably adjusting the vibration amplitude or the nominal clearance of the bearing. In addition, the results indicate that the direct stiffness and damping coefficients are increased by decreasing the rotation speed or increasing the vibration amplitude of the bearing pad.