AN ANALYSIS OF GAS-LUBRICATED FOIL-JOURNAL BEARINGS

The foil journal bearing is essentially a series of thin overlapping circular metal foils, one end of which is cantilevered to the bearing and the other end rests on an adjacent foil. Typically, the radial load at the high temperature end (turbine) of a gas turbine engine is supported by a roller bearing. The high temperatures encountered at the turbine end result in reduced roller bearing life and also necessitate elaborate cooling and lubricating systems to keep the bearing temperatures within reasonable limits. Foil-journal bearings are simple, lightweight and well suited for such high temperature applications, and since they are self-acting air bearings the need for a lubricant supply system is obviated. The hydrodynamic pressure force in the air film generated by the journal rotation deflects the compliant foil surface resulting in a change in film thickness, and hence the pressure solution to the problem is of the elasto-hydro-dynamic (EHD) type. The nonlinear compressible finite-length Reynolds equation is numerically solved (finite difference method) in conjunction with the elasticity equations governing the foil surface deflections using an iterative scheme. The elasticity solution accounts for area contact between foils. Because of several levels of iteration involved, the EHD solution requires considerable computational effort. Gas-film pressure and film thickness distributions, EHD solution convergence characteristics, bearing load capacity, etc. are presented as a function of journal speed and eccentricity.