Theoretical And Experimental Research Of Gas Foil Bearing

Foil bearings are self-acting hydrodynamic gas bearings with elastic components as the supporting structure and have many advantages such as high operating speeds, no contamination, lower frictional loss, long life, wide operating temperature range, improved stability and good adaptivity et al. Compared with the traditional rigid surface bearings and rolling element bearings, foil bearings have significant and wide application value in the fields including cryogenics and refrigeration, aerospace and national defense. In this dissertation, an area contact mechanics model is built up to replace the traditional line contact model for better performance prediction of multileaf gas foil bearings. The mechanism of area contact on the bearing performance is revealed, and the test-bed is designed and established for the experimental study. Meanwhile, systematical theoretical and experimental research is conducted to analyze the influence of key factors on the bearing performance.According to the geometry of foil journal bearing, the foils are simplified as cantilevered curved beams, and the geometric relationship of overlapping foils is obtained. Then the Castigliano second theorem is adopted to derive the formula for the foil deformation. The area contact model is built up in which the constraints of foil deformation must be satisfied. Then the relationship between gas film forces and interaction forces between foils are obtained, and the whole stiffness matrix of the foil structure is established. Meanwhile, the deformation of all foils can be calculated with the known force condition of foils. The weighted residual method and finite element method are used to calculate the pressure distribution of gas film, and an algorithm is developed to judge and determine the contact condition of adjacent foils. A flowchart is built up to calculate the converged elastohydrodynamic(EHD) solution based on the area contact model. Using the perturbation method, the relationship among foil deformation, film thickness and pressure distribution is obtained, and the finite difference method is adopted to discretize the Reynolds equation for calculating the stiffness and damping coefficients.On the basis of aforementioned area contact model, the static and dynamic performances are calculated, and the simulation results are in agreementment with the published experimental results, which shows the correctness and applicability of this method. Furthermore, the effects of foil thickness, central angle, setting angle, aspect ratio, radial clearance, rotating speed and eccentricity ratio on the bearing performance are analyzed. Through the analysis of simulation results, the evolutional mechanism of area contact and its influence on load carrying capacity is revealed. The results show that the occurrence of area contact is beneficial to improve the load carrying capacity of the multileaf foil bearings.For foil thrust bearings, the elastic thin plate theory and Heshmat model are used to build up the stiffness matrixes of top foil and bump foil, which are combined together to form the global stiffness matrix of the supporting structure. Then the equation of gas film thickness is established considering the parameters of supporting structure, ramp slope, bump consistency and foil deformation. The Reynolds equation is solved in the cylindrical coordinate system by the similar method applied to the journal bearing, and a flowchart is also built up to predict the bearing performance.Based on the established model, the static and dynamic performances of foil thrust bearings are calculated, and the effects of the parameters of supporting structure, ramp slope, bump consistency and operating parameters are analyzed. Meanwhile, the bearing parameters are optimized to improve the load carrying capacity.On the basis of the theoretical analysis and simulation results, the testing programs are designed for the multileaf gas foil journal bearing and the bump-type gas foil thrust bearing respectively, which include the physical design of test-beds, the design and manufacturing of test-bearings and the construction of measurement system. The loading-unloading experiment at the null speed and high-speed operating experiment are conducted. The effects of bearing design parameters and operating parameters on the load carrying capacity and frictional torque are analyzed, which can provide guidance for the further parameter optimization and performance improvement of the bearings.The area contact model and corresponding numerical algorithm proposed in the dissertation can accurately predict the load carrying capacity and improve the theoretical system of foil bearing, which are helpful for promoting the futher development and application of the multileaf gas foil bearing. The deep studies of gas foil thrust bearings contributes to improve the bearing properties.