Finite Element Analysis of Gas Foil Bearings

Abstract

Micro turbomachinery demands gas bearings to be light compact and should operate at varying temperature conditions. Low heat generation friction and lack of lubricant circulation system makes it compact reliable and eco-friendly. However low stiffness and damping coefficients, high cost and lack of sufficient knowledge and predictive tools somewhat restricts GFBs use in mass produced application. Current commercial and engineering application demands more and more aggressive designs with high surface speed and unit loads as well as thinner fluid film. Again rotor-dynamics analysis uses stiffness and damping coefficients to represent fluid film behavior or in other words these coefficients play the key role in determining dynamic characteristics of a rotor shaft. Stiffness coefficients depend mainly on two factors first the static deflection of foil due to shaft load and second the hydrodynamic effect produced due to the fluid film. Here is an approach to calculate the stiffness coefficient produced due to static deflection of GFBs due to static load using finite element analysis and the stiffness coefficient has been calculated. Reynold’s equation is to be solved using FDM to obtain pressure profile during hydrodynamic action of fluid film and using these pressure values in the bearing model dynamic component of stiffness can be produced. Adding both components will produce the overall stiffness coefficient of a gas foil bearing.