Foil bearings can enable different turbomachinery architecture. The use of the cycle's working fluid within the bearings results in an oil-free and compact turbomachinery system. Using CO 2 as the operating fluid for a foil bearing creates new operating and new modelling challenges. These include turbulent flow within the film, non-negligible inertia forces, high windage losses, non-ideal gas behaviour and reduced rotordynamic damping. Since the flow phenomena within foil bearings are complex, involving fluid flow, structural deformation and heat transfer, use of the conventional Reynolds equation is not proven to be suitable for foil bearings with CO 2 as the operating fluid. To address these modelling issues, a multi-physics multi-timescale simulation tool including fluid, structure and thermal solvers was developed to predict the performance of foil bearings and to create insight on their operations with CO 2. New flow physics and operation challenges for foil thrust bearings with