Tianwei Lai

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

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 −20 µm clearance, while unstable operation appears with 80 µm 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.

Static characteristics of six pads multilayer protuberant foil thrust bearings

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.

Comparative studies on double-layered protuberant foil bearing and Hydresil foil bearing

In this paper, the hydrodynamic performance of a new double-layered protuberant gas foil journal bearing (DPGFB) was experimentally studied in a high-speed turbo-expander and compared with the conventional Hydresil foil journal bearing (HGFB). The material properties of supporting foils are important for the bearing performance such as load capacity and frictional damping. In both DPGFBs and HGFBs, two types of materials, stainless steel (0Cr18Ni9) and beryllium bronze (QBe1.7), have been used as supporting foil materials, and their effects on the bearing performance were discussed. A stable operation of turbo-expander with rotational speed up to 70,000 rpm was achieved in the tests of both of two types of bearings. Due to the larger stiffness of the foil layer, the DPGFBs had larger lift-off speed and larger gas film friction torque than HGFBs at high speed when the same foil material was used. The comparison showed that the bearings using 0Cr18Ni9 had a larger life-off friction torque. The synchronous vibration amplitudes of the rotors during the high speed operation and the shut-down process were smaller for DPGFBs than HGFBs, which indicated that the DPGFBs had a better damping performance than HGFBs.

Numerical analysis of the static performance of an annular aerostatic gas thrust bearing applied in the cryogenic turbo-expander of the EAST subsystem

The EAST superconducting tokamak, an advanced steady-state plasma physics experimental device, has been built at the Institute of Plasma Physics, Chinese Academy of Sciences. All the toroidal field magnets and poloidal field magnets, made of NbTi/Cu cable-in-conduit conductor, are cooled with forced flow supercritical helium at 3.8 K. The cryogenic system of EAST consists of a 2 kW/4 K helium refrigerator and a helium distribution system for the cooling of coils, structures, thermal shields, bus-lines, etc. The high-speed turbo-expander is an important refrigerating component of the EAST cryogenic system. In the turbo-expander, the axial supporting technology is critical for the smooth operation of the rotor bearing system. In this paper, hydrostatic thrust bearings are designed based on the axial load of the turbo-expander. Thereafter, a computational fluid dynamics-based numerical model of the aerostatic thrust bearing is set up to evaluate the bearing performance. Tilting effect on the pressure distribution and bearing load is analyzed for the thrust bearing. Bearing load and stiffness are compared with different static supply pressures. The net force from the thrust bearings can be calculated for different combinations of bearing clearance and supply pressure.

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

Foil bearing provides compliant support and moderate Coulomb friction for rotor-bearing system, which is conducive to stability and reliability of high speed rotating machinery. In this paper, both hydrodynamic lubricated foil journal and foil thrust bearings are applied in a 150 m3·h−1 turboexpander for air separation. In the bearings, protuberant foil is chosen as the supporting subfoil due to its merits of easy fabrication and assembly. Static loading and deflection of the bearings are tested, respectively, before integration into the turboexpander. Afterwards, the loading and deflection curves of the journal and thrust bearings are polynomial fitted using least-square method. Then, performance tests are carried out on the rotor-bearing system, including transient speed-up, high speed, and speed-down processes. In the tests, the turboexpander supported by the hydrodynamic foil bearings operates smoothly with repeatability. Maximal rotor speed of the turboexpander reaches 52000 rpm with hydrodynamic lubricated protuberant foil bearings.