Effects of bearing clearance and supporting stiffness on performances of rotor-bearing system with multi-decked protuberant gas foil journal bearing

Abstract

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.

Development and Application of Integrated Aerodynamic Protuberant Foil Journal and Thrust Bearing in Turboexpander

“…With increase of rotor speed, the amplitude of nonsynchronous vibration around 100 Hz increases and cluttered trajectory appears at around 50000 rpm. With increase of rotor speed, its amplitude increases from less than 0.5 m to around 1 m. Similar to the tested results in [31], the rotor locus also becomes cluttered around 90 krpm when the bearing clearance is larger than 80 m with protuberant foil thickness of 0.07 mm. In this paper, the nonsynchronous vibrations are more obvious, which could be attributed to the larger nominal bearing clearance.…”

“…In all three directions, there are nonsynchronous vibrations around 100 Hz. In radial directions and , the nonsynchronous vibration amplitudes are larger comparing to the cascade plot of the rotor supported with foil journal bearing and aerostatic thrust bearing in reference [31]. When the rotor speed is larger than 50000 rpm, the nonsynchronous vibration amplitude increases and exhibits speed dependency.…”

“…The landing speed of the rotor on the foil bearing is around 6000 rpm, which is smaller than that of lift-off speed of 9600 rpm. This can be attributed to the friction effect between the foils during the speed-up and speed-down processes [31]. The resting location of the rotor after coast-down is (103, 272 ∘ ).…”

“…In order to validate the applicability of integrated aerodynamic foil bearing supporting technology in this turboexpander, the test rig of high speed turboexpander is retrofitted based on the rig in reference [31]. The flow chart of gas driven test rig is shown in Figure 3.…”

Experimental study on multi-decked protuberant foil thrust bearing with different number of thrust pads

“…The projections on the protuberant foils were fabricated by punching from a plain foil. For the protuberant foil journal bearing, the subsychronous vibrations could be suppressed effectively since its first application in a high speed turbo-expander (Lai et al, 2014). Therefore, similar configuration was introduced in thrust bearing.…”