Validation of a three-dimensional CFD analysis of foil bearings with supercritical CO2

Foil bearings are an integral part of oil-free turbomachines which have been selected as a potential technology to enable cost efficient Supercritical Carbon Dioxide Brayton cycle for solar power application. Using high pressure CO2 as the operating fluid means that within the film Reynolds numbers in the highly turbulent regime are observed, therefore, using traditional simulation tools, such as two-dimensional Reynolds equation, derived for simulating bearing operating with laminar flow is not appropriate. The resulting turbulence enhances hydrodynamic load capacity and increases frictional losses. In this study, some improvements such as moving wall and periodic boundary conditions to the UQ in-house CFD code Eilmer are presented. These are verified using Taylor-Couette flow, and axisymmetric and wavy Taylor vortices are simulated under different Taylor number. A hydrostatic air thrust bearing with steady-state behaviour is also studied, which shows good agreement with the results from modified Reynolds equation. Finally, a preliminary Three-Dimensional Computational Fluid Dynamic simulation of a foil bearings is presented. A rigid foil bearing is studied with ambient air and high pressure CO2 as operating fluid, respectively and the lift force and power loss are compared with the results from Reynolds equation.

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