Dynamic Stiffness and Damping of Foil Bearings for Gas Turbine Engines 931449

Foil bearings have been used since the 1970s in low temperature (600F) applications. However, adapting this type of hydrodynamic air bearing to the high temperature (1 200F) environment of gas turbine engines has been slow, due to suspected low damping values. Foil bearings develop mechanical interactions, thought to generate coulomb damping, which affects the dynamic characteristics - dynamic stiffness and damping, the primary factors influencing dynamic stability of rotor-bearing systems - of such a bearing. This paper reports on a program of experiments to identify the design parameters affecting foil bearing dynamics. A fractional factorial technique characterized the effects of the primary independent design parameters and their interactions. Results are presented for eight test bearings, with an analysis of variance used to determine the optimum configuration and show how it can improve the stability of a typical gas turbine engine.