Analysis of foil journal bearings with backing springs

Gas-lubricated foil journal bearings are simple in construction, lightweight and well suited for high-temperature applications in turbomachinery. Bearing stiffness is governed primarily by the foil flexural stiffness. The bearing consists essentially of thin overlapping circular metal foils, one end of which is cantilevered to the bearing housing and the other end rests on an adjacent foil. An analysis of gas-lubricated foil bearings is presented with a specific type of backing spring used under the foils to control bearing preload and stiffness. The backing spring acts like an elastic foundation under the foil and radically changes the hydrodynamic pressure distribution generated in the gas film. The pressure distribution is obtained by simultaneously solving the compressible Reynolds equation and the elasticity equations governing the compliant bearing surface, consisting of foils and backing springs. An iterative scheme is used to obtain pressure distributions for heavily loaded cases, involving extensive computation, because of the sensitivity of pressure solution to small changes in film thickness distributions attributable to the compliant bearing surface. Pressure distribution, film thickness, bearing load capacity, iterative solution convergence characteristics and bearing power dissipation are presented as a function of journal eccentricity.