Colloquia

Summary

Abstract:

Air foil bearings are increasingly favored in high-speed turbomachinery due to their ability to operate in high-temperature environments (up to 873 K) without contamination. This thesis evaluates the thermal stability and load-carrying capacity of an 8-pad air foil thrust bearing operating at 100,000 rpm in a Mitsubishi fuel cell turbocharger. The bearing uses on a thin air film, typically measured in tenths of microns, formed through hydrodynamic lubrication and supported by bump foils to generate pressure and support loads.

The study is divided into three phases of simulations conducted in Ansys. In Phase 1, the Fluent setup for a 6-pad bearing is validated by comparing the results with MATLAB simulations from a previous study. Phases 2 and 3 then focus on the 8-pad bearing at 100,000 rpm. Phase 2 investigates the effect of cooling flow rate on bearing performance and heat transfer, particularly in a configuration with a 40-7 μm gap height. The results show that increasing the cooling flow reduces the air film’s temperature, enhancing thermal stability but also decreasing the bearing's load-carrying capacity.

Phase 3 examines the influence of geometric parameters on bearing performance, concluding that the highest load-carrying capacity is achieved when the hydrodynamic wedge is centered on the pad and when the wedge inclination is high, resulting in the smallest possible nominal gap height (h2) of the air film.