ANALYSIS OF FOIL JOURNAL BEARINGS WITH BACKING SPRINGS

Gas-lubricated foil journal bearings are simple in construction, light weight and well suited for high-temperature applications in turbomachi nery. Bearing stiffness is governed primarily by the foil flexural sti ffness. The bearing consists essentially of thin overlapping circular metal foils, one end of which is cantilevered to the bearing housing a nd the other end rests on an adjacent foil. An analysis of gas-lubrica ted foil bearings is presented with a specific type of backing spring used under the foils to control bearing preload and stiffness. The bac king spring acts like an elastic foundation under the foil and radical ly 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 gover ning the compliant bearing surface, consisting of foils and backing sp rings. An iterative scheme is used to obtain pressure distributions fo r heavily loaded cases, involving extensive computation, because of th e 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 solutio n convergence characteristics and bearing power dissipation are presen ted as a function of journal eccentricity.