This paper presents comprehensive test measurements for gas journal bearings with damping structures of a bump foil layer and/or a polymer layer. A one-pad top foil forms the bearing surface, under which the bearing structure and a bearing housing are located. Test bearings include gas foil bearings (GFBs), gas polymer bearings (GPBs), and gas foil-polymer bearings (GFPBs). In addition, three metal shims were employed to create wedge effects in the GFPBs. Firstly, static load-deflection tests of test bearings estimate the radial assembly clearance, which is measured to be ∼200 μm. Secondly, shake dynamic loading tests identify frequency-dependent dynamic characteristics. An electromagnetic shaker provides flat bearing specimens with one-degree-of-freedom vertical dynamic loading at excitation frequencies reaching 800 Hz. The bearing structures of GFB, GPB, and GFPB were measured to have resonance frequencies near 200 Hz. The GFPB has the lowest stiffness coefficients, which also increased with increasing excitation frequency. In addition, it has higher loss factor than those of GFB, which decreases with increasing excitation frequency. Therefore, GFPB was measured to exhibit a higher structural damping and lower stiffness than GFB. Lastly, the electric motor driving tests examine the rotordynamic stability performance. A permanent magnet (PM) synchronous motor drives a PM rotor supported on a pair of test journal bearings. The rotor has a diameter of 40 mm, length of 240 mm, and weight of 19.6 N. Two orthogonally positioned displacement sensors record the horizontal and vertical rotor motions. Test results indicate that sub-synchronous rotor motions for GFPBs showed the lowest amplitudes < 28 μm with the WFRs ∼0.14, and operated up to the highest rotating speed of 85 krpm with the OSS of 69 krpm, compared to GFBs and GPBs. In addition, the effects of mechanical preload and bearing clearance on the rotordynamic performance are examined for GFPBs. As a result, the GFPBs with mechanical preloads enhanced the rotordynamic performance with no subsynchronous motions up to the maximum rotor speed of 88 krpm, and the bearing friction characteristics as well. Furthermore, they showed comparable rotordynamic performance to three-pad GFBs from a past literature, even with larger bearing clearances and small mechanical preloads.

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