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

The commitment to environmentally friendly transportation calls for efficient solutions with the evolution of automotive industry. Turbochargers are an important part of this development. The application of Gas or Air Foil Bearings (GFB) instead of traditional hydrodynamic bearings is recently very noticed, with which the fuel consumption, and emissions can be minimized as well as decreasing the maintenance costs and increasing the 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 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. Two methods of computing the static pressure distribution are evaluated and compared through a detailed static analysis considering the influence of different parameters i.e., eccentricity, clearance, rotor speed and foil compliance of the GFBs on the load carrying capacity. Next, the influence of different parameters of the GFBs on the dynamic stiffness and damping coefficients is also presented.