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.

No abstract

Foil bearing is considered to be a promising supporting technology in high-speed centrifugal machinery. Due to the high-speed shearing effect in the viscous lubricant film, heat generation could not be ignored. In this paper, a thermo-elastic model of the multi-leaf foil thrust bearing is proposed to predict its thermal and static characteristics. In the model, modified Reynolds equation, energy equation, and Kirchhoff equation are solved in a coupling way. The contact area between the foil and welding plate is taken into account. Besides, the effect of cooling air on the bearing temperature is investigated. The ultimate load capacity and transient overload failure process of the bearing is analyzed and discussed. The effect of rotation speed on the bearing temperature is more obvious than that of the bearing load. The bearing temperature drops obviously by introducing the cooling air, and the cooling effect is improved with the supply pressure. The transient overload failure of the bearing occurs when the bearing load exceeds the ultimate value.

No abstract

No abstract

A type of foil journal bearings with double-layer protuberant foils as elastic support was studied by numerical analysis and experiments. Two kinds of material (beryllium bronze and stainless steel) with different elasticity were used for the protuberant foils of the bearings. The analyzing model couples the hydrodynamics pressure of the gas film to the elastic deflection of the top foil and the underlying protuberant foils. The hydrodynamics of gas film is described by the Reynolds equation. The top foil and the protuberant foils are modeled as thin plates and the protuberances are treated as rigid support. For calculating the deflection of the top foil, the deflection of the protuberant layer beneath the top foil is taken into account. With a given load, the gas film thickness and pressure are obtained by using finite element method and finite difference method. The key static and dynamic parameters are presented. In experiments, both of the two foil bearings run well in a turbo-expander. The new takeoff and shutoff pressure and speed are proposed for practical operation of the hydrodynamic lubricated high speed turbo-expander. In addition, the synchronous and subsynchronous rotor motions have been tested and analyzed. The experimental tests of the two bearings in a high-speed turbo-expander suggest that the bearing using stainless steel as the foil material shows higher stiffness, which agrees well with the numerical predictions.

In the fluid film lubrication of high speed turbomachinery, bearing performance plays a significant role in the dynamics of the rotor-bearing system. In this paper, a novel foil thrust bearing using multi-decked protuberant foils as supporting structure is developed and tested. Experimental bearing test rig using gas-driven high speed turbo-expander is set up to evaluate static loading characteristics of the bearing. Static stiffness, friction torque, nominal bearing clearance and axial vibration amplitude are discussed in the transient processes. Static loading characteristic of the bearing is evaluated based on the relationship between displacement and loading force. Test results indicate that this simply configured thrust bearing has a good prospect in high speed hydrodynamic lubrication.