Walton II, J.F. and Heshmat, H. “Compliant Foil Bearings for Use in Cryogenic Turbopumps,” Advanced Earth-to-Orbit Propulsion Technology Conference held at NASA/MSFC, May 17-19, 1994, (1994) NASA CP3282, Volume 1, pp. 372-381.
The feasibility of replacing cryogenic turbopump rolling element bearings with compliant foil bearings (CFBs) is examined. Foil bearings, in addition to long life, can be designed to provide desired stiffness and damping characteristics necessary for optimum turbopump rotordynamic characteristics. While predicted bearing load capacity for a hydrodynamic LOX CFB exceeds 300 psi, the high loads associated with the SSME HPOTP dictate that a hybrid CFB combining hydrostatic and hydrodynamic principles, be considered if direct bearing substitution is planned.
As confirmation of CFBs potential for application in high speed turbopumps, recent advances in foil bearing performance are presented. Achieved load capacities approaching 100 psi in air readily indicate that the predicted load capacities in excess of 300 psi are possible in liquid cryogens. Dynamic characterization of foil bearing structural damping has demonstrated damping capability up to 40 lb-sec/in. The benefits of both increased load capacity and damping in a CFB are demonstrated in rotordynamic testing to 50,000 rpm, or approximately 50% beyond the 34,020 rpm first bending critical speed of a test rotor-bearing system.