Characteristic Analysis And Experimental Study Of Aerodynamic Foil Journal Bearings

Aerodynamic foil journal bearing is a kind of self-acting hydrodynamic bearing with flexiblesurface for supporting. It consists of three parts: a smooth top foil that provides the bearing surface, abump foil that acts as an elastic foundation and a housing for fixing. This type of bearing offersseveral advantages over the traditional gas bearing, including long operating life and reliability, higherload capacity, higher temperature capability, and higher operating speed, etc.This thesis focuses attention on Hydresil-type bump foil bearing. Shell model is adopted tocalculate the stiffness of the bump foil. Finite difference method and the Newton-Raphson iterationmethod are both applied to solve the coupled pressure governing Reynolds equation and gas filmthickness equation. The influences of speed as well as eccentricity on bearing capacity, attitude angleand friction torque are analyzed.By the use of small perturbation method, the film thickness, pressure and foil deflection areexpressed in terms of a small displacement and a small velocity at the equilibrium position in Taylorseries expansions, which are substituted into Reynolds equation and gas film thickness equation,equations related to the differential pressure and film thickness are achieved. In terms of the balancerelation among pressure, foil deformation and film thickness, other differential equations are achieved.The stiffness and damping coefficients could be obtained by solving these equations. The influencesof the eccentricity ratio, the shaft speed and the whirl frequency on the dynamic coefficients have alsobeen discussed.Considering the heat convection between the gas flow and the top foil as well as the journal, andthe viscosity-temperature relationship of air, a simplified3D lubrication gas heat transfer model isestablished. The temperature distribution of the gas film is then obtained by solving the discreteenergy equation.A special foil bearing performance test-rig was built. The test-rig includes test bearing, lubricatingand cooling system, and measure system. Top foil and bump foil made of beryllium bronze are shapedin a special mould. The vibration characteristics of the shaft were measured. The radial displacement,the friction as well as the temperature distribution of the bearing were measured under conditions ofdifferent loads and rotational speeds.