The multilayer protuberant foil bearing, as a new type of compliant surface foil bearing, shows a great and wide application promise. Six pads multilayer protuberant foil thrust bearings with different configurations were designed and fabricated in this study. The static characteristics of these bearings and the effects of their key configuration parameters including the thickness of top foil, the thickness of protuberant foil, and the layers of protuberant foil are investigated. The experimental results reveal that the bearings show nonconstant structural stiffness, and the stiffness mainly depends on both the load force and the configuration of the bearings. In the airborne regime, the torque of the bearing is mainly dependent on the load force rather than the rotational speed, which can be interpreted by the proportional relationship between the bearing clearance and the rotational speed. Furthermore, the experimental results also show that the maximum load capacities of the bearing are also greatly affected by the bearing configuration. With more layers of the protuberant foils and thinner top foil, the bearing shows larger maximum load capacity. The work provides some insights about the relationships between the characteristics and the configuration of the bearings.
The supporting stiffness and coulomb damping in a bearing play significant roles in the smooth operation of rotor-bearing system. The performance of multi-decked protuberant gas foil journal bearing is evaluated experimentally in a high-speed turboexpander. The effect of radial clearance on the bearing performance is analyzed based on the relationship between rotor speed and supply pressure in the speed-up and speed-down processes. The maximal speed of the 25 mm diameter rotor reached as high as 100 kr/min, and subsynchronous vibrations are suppressed in the tests. For the bearings with 0.05 mm protuberant foils, there will be thermal runaway problem with À20 mm clearance, while unstable operation appears with 80 mm clearance. For the bearing with 0.07 mm protuberant foil, the vibration amplitude is constrained within smaller amplitude due to stiffer supporting structure. The test results indicate that the bearing can operate stably under different gas film thickness and supporting stiffness, and that this kind of foil bearing can be applied in high-speed turbomachinery due to its stability and adaptability.
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