Theoretical Analyses And Experimental Investigations Of A Gas Foil Bearing With Nested Compression Springs

Gas foil bearing(GFB), as a type of self-acting hydrodynamic air bearing, exhibits a series of advantages over ball bearings or oil-lubricated bearings, such as higher rotor speed operation, extreme temperature capabilities, and reduced maintenance. The applications of GFBs include air cycle machines, auxiliary power units, cryogenic turboexpanders, air compressors, and fuel cell blowers. Despite the significant potential of GFBs, there are also some shortcomings that prevent their extensive use, such as insufficient load and damping capacity, complicated supporting structure. In order to overcome these shortcomings and improve the performance of GFBs, this paper introduced and designed a novel gas foil bearing with nested compression springs(NSFB). This type of gas foil bearing is easily manufactured and can provide good load and damping performance. The main contents of this paper are as follows:The structural characteristics of NSFB are investigated. An analytical model, which considered the effects of interaction and friction between adjacent springs, was established to predict the structural characteristics of the compliant structure. Static and dynamic tests were conducted to analyze the structural performance of NSFBs. The predicted hysteresis loop of the compliant structur e corresponded well with the measured results from the pull–push tests. A static test result comparison between an NSFB and a bump-type gas foil bearing(BFB) showed that the NSFB had a larger loss factor, which implied its superior damping performance. Th e effects of spring number and axial preload between adjacent springs on bearing performance were investigated.The static performance of NSFB based on the proposed analytical model was predicted and analyzed. The stiffness matrix of compliant supporting structure, which considered the stiffness of top foil, was established. The finite-difference method and Newton-Raphson iteration method were used to solve the steady-state Reynolds equation. The gas pressure and film thickness distribution were obtained by coupling the stiffness matrix of compliant supporting structure and gas pressure. The effects of spring number, rotor rotational speed and static load on the static performance of NSFB were investigated. Finally the effect of axial stiffness distribution of compliant supporting structure on the load capacity of NSFB was investigated.On the basis of static performance analysis of NSFB, the dynamic performance of NSFB was predicted and analyzed. The equilibrium equation of compliant supporting structure based on the proposed analytical model of nested spring structure was established. One steady-state Reynolds equation and four linearized dynamic coefficient equations were obtained b y using the perturbation method. The four stiffness and the four damping coefficients were obtained by using the finite difference formulation to solve these dynamic equations. The effects of rotor rotational speed, axial preload and spring number on the stiffness and damping coefficients were investigated.The performance of NSFB after lift-off was evaluated and analyzed. The drag torque and temperature of NSFB at a constant rotational speed was measured. The measurement results show that the bearing lifted off successfully. A test rig used to conduct the push-pull test after the bearing lift-off was established. The push-pull test at different rotor rotational speed and different spring number was conducted to investigate the performance of NSFB.