Prediction of Stiffness Coefficients for Foil Air Bearings to Perform Rotordynamic Analysis of Turbomachinery

Abstract

This paper studies foil gas bearings for the small-size high-speed turbomachinery applications. The main part of the work is devoted to the modeling of the foil gas bearings using computational fluid dynamics (CFD). Deformation of compliant elements is incorporated directly into the CFD model by means of analytical expressions and moving mesh technique. The CFD model is used to predict load capacity and rotordynamic stiffness coefficients of the foil bearing. The studied bearing is a multi-leaf foil bearing with four foils mounted on the elastic layer. The radial deflection of the elastic layer depends on the gauge pressure in the gas film. Results are presented for the rigid bearing and the foil bearing for the eccentricity ratios of 0.75, 1.0, 1.5. Information on computational costs, usability, and validity of the presented CFD-based approach is given. Application of an alternative model of foil bearing based on the Reynolds equation is also discussed.