Aerodynamic and Thermal Behaviour of Helium Lubricated Gas Foil Journal Bearing for High-Speed Cryogenic Turboexpander

Abstract

Gas Foil Bearings (GFBs) are used for several high-speed applications such as cryogenic turboexpander and turbochargers in order to achieve desired load carrying capacity with better stiffness and damping characteristics. The present work deals with the aerodynamic analysis of helium lubricated bump-type gas foil journal bearing of 16 mm diameter at a design speed of nearly 240krpm. The numerical model is developed by using the non-linear compressible Reynold’s equation and structural equations. Both the equations are coupled to predict the aerodynamic pressure, film thickness and load carrying capacity. The coupled equation is discretized in second order using the finite difference method and solved using successive over-relaxation (SOR) method for quick convergence. A detailed comparison is made between a rigid and compliant journal bearing to verify the advantages of GFBs and its feasibility in the current application. The effects of varying eccentricity on the aerodynamic characteristics are also presented along with mid-plane normalized pressure profile and film thickness. The work is further extended to predict the temperature distribution over gas foil journal bearing using energy equation.