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This paper surveys two bearing approaches that may be considered for gas turbine applications. The first is the hybrid bearing which uses a fluid film in parallel or in series with the rolling-element bearing, and whose objective is to increase the L10 life of the rolling-element bearing in high-load and/or high-speed applications. In the parallel arrangement this objective is sought by load sharing between the fluid-film and rolling-element bearing components. In the series arrangement, the objective is sought by achieving a decrease in the effective speed of the rolling-element bearing. The series approach also provides radial, viscous, damping, and this paper derives the relationships necessary for such design. The second approach is the use of gas bearings as a solution to problems of high-temperature operation. The merits and potential problem areas of gas bearings in advanced gas turbine applications are discussed and some appropriate gas bearing types are described.

This paper discusses the influence of rolling element and fluid film bearings on rotor dynamics of “high-speed” turbo-machinery. System critical speeds, rotor response to unbalance, instability, and turbulence are discussed. The types of fluid film bearings best suited for high-speed operation are identified. Examples of high-speed turbomachinery using rolling element, liquid film and gas bearings are presented.

This paper presents the results of studies which demonstrate the feasibility of the High-Frequency Resonance Technique for defect analysis of rolling-element bearings in virtually any bearing system. Specific emphasis was placed on helicopter engine and transmission applications. The HFRT is a method for separating ball-pass or roller-pass frequency peaks from background noise by isolating and demodulating high frequency spectrums of accelerometer signals. The process is also called envelope detection. Tests were conducted with bearings from a UH-1 helicopter transmission to show the effectiveness of the HFRT explicitly for that application and implicitly for other bearing applications. The resonance peaks for these tests were selected by inspection of raw data signals and were found to correlate reasonably well with predictable bearing race natural frequencies.