Hydrostatic air foil bearings: Analytical and experimental investigation

Abstract

Air foil bearings have been used in various micro-turbomachinery applications. One of the critical technical challenges in extending the operating envelope of the air foil bearing to larger systems than current applications is the issue of coating wear on the top foil and rotor during starts/stops. This paper reports the design, construction, and testing of the first hydrostatic air foil bearing (HAFB). The HAFB showed higher load capacity with much less air consumption than the hydrodynamic counterpart, which is a noticeable advantage of HAFB in efficiency and cooling capacity. In addition, start torque was very small and comparable to the friction torque of steady-state hydrodynamic operation. The small start torque clearly indicates that the HAFB can help to eliminate the wear problem that has been a chronic failure mode in heavily loaded air foil bearings. A simple analytical model for prediction of top foil deflection and sagging effects under hybrid (both hydrostatic and hydrodynamic) mode was developed. The new top foil deflection model showed very good agreement with published experimental data. The top-foil deflection model and associated bump dynamics were integrated into time-domain orbit simulations to predict imbalance responses of a rigid rotor supported by HAFBs.