Numerical Study of Application of Gas Foil Bearings in High-Speed Drivelines 2024-01-2941

Gas bearings are an effective solution to high-speed rotor applications for its contamination free, reduced maintenance and higher reliability. However, low viscosity of gas leads to lower dynamic stiffness and damping characteristics resulting in low load carrying capacity and instability at higher speeds. Gas bearings can be enhanced by adding a foil structure commonly known as gas foil bearings (GFBs), whose dynamic stiffness can be tailored by modifying the geometry and the material properties resulting in better stability and higher load carrying capacity. A detailed study is required to assess the performance of high-speed rotor systems supported on GFBs, therefore in this study a bump type GFB is analyzed for its static and dynamic characteristics. The static characteristics are obtained by solving the non-linear Reynolds equation through an iterative procedure. The dynamic characteristics i.e., stiffness and damping coefficients are obtained through a perturbation method, also a direct method to evaluate the stiffness coefficients is obtained and compared. Finite difference method (FDM) is used to solve the system of equations numerically. An initial static analysis of the GFBs is presented to study the load carrying capacity and the pressure distribution under the influence of different parameters i.e., eccentricity, clearance and the rotor speed. The influence of the foil geometry and material properties of the GFBs on the dynamic stiffness and damping coefficients is also studied. Next, a dynamic analysis of the rotor bearing system with the calculated dynamic coefficients is studied through the Campbell diagrams, mode shapes, steady state frequency response for an unbalanced force and a transient response.