A foil bearing is a self acting hydrodynamic device capable of separating rotating components of high speed turbomachinery by a film of air or other gaseous lubricant. It was originally discovered over one-half century ago by Block and VonRussom [1]. The benefits of such bearings in aerospace applications can be quite significant. The benefits of foil bearing supported machines include: reduced machine weight due to the elimination of the oil systems, removal of the traditional diameter-rotational speed limit imposed by rolling element bearings, and a synergistic use of working fluid as a lubricant enabling a contaminant free working fluid [2]. However in order to realize these benefits, foil bearing must be able to support the required machine load and operate reliably and without burden to the machine. Excess burden to a turbomachine typically manifests itself in the detrimental use of working fluid as bleed flow to cool or pressurize specific components. Current modeling techniques for preloaded gas foil journal bearings do not provide accurate results in the lightly loaded region of operation. The primary cause of this modeling pitfall is the use of a fictitious clearance in the hydrodynamic calculations. A physics-based approach is taken to overcome this critical modeling deficiency.
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