A Full Three-Dimensional Transient Fluid-Structure Interaction Model for the Dynamic Characteristics Predictions of Bump-Type Gas Foil Journal Bearings

Abstract

Abstract Oil-lubricated bearings are used in most present-day rotating machinery due to their high load capacity. This bearing, however, requires a complicated lubrication system which significantly increases the operating cost of the equipment. Moreover, the problem of the heat generation of lubricated oil after a long time of operation cannot be ignored, especially in high-speed turbomachinery. As for oil-free turbomachinery, the gas-lubricated bearing is regarded as a revolutionary technology to support the rotor. Bump-type gas foil bearing (bump-type GFB) is one of the most widely used gas-lubricated bearings, due to its high speed, low wear, no pollution, high temperature and pressure resistance and other excellent properties. As one of the critical components in the rotor system of a rotating machinery, bump-type GFBs can provide not only the static load capacity but also the dynamic gas film response forces, significantly affecting the dynamic stability performance of the rotor system. Therefore, an accurate and efficient dynamic characteristics prediction method for bump-type GFBs is crucial for the industrial safe operation of the rotating machinery system. This paper focuses on the assessment and validation of a novel numerical method for the dynamic coefficients prediction of bump-type gas foil journal bearings (bump-type GFJBs). To predict the dynamic characteristics of bump-type GFJBs, in this paper, a novel full three-dimensional (3D) transient fluid-structure coupled numerical method was proposed, based on the finite element analysis (FEA) and the computational fluid dynamics (CFD). In order to improve computational efficiency and conform more to the bearing actual situations, a multiple-frequency elliptical-orbit rotor whirling model for arbitrary eccentric positions was proposed to define the rotor whirling motion, based on the mesh deformation techniques. The present full 3D transient CFD/FEA method was validated by the published experimental data of the dynamic stiffness and damping coefficients of a bump-type GFJB. The influences of the disturbance frequency and foil deformation on the dynamic characteristics of bump-type GFJBs were also presented and discussed. The results indicate that the dynamic characteristics predicted by the present method has reasonable accuracy compared to the experimental results. The dynamic performance of the bearing is influenced by both the gas film and the foil structure. The foil structure adjusts the thickness and pressure distribution of the gas film through the foil deformation to change the dynamic performance of the bump-type GFJBs. The bump-type GFJB has a positive energy dissipation factor so that the rotor-bearing system supported by bump-type GFJBs has the ability to comeback and remain stable.