Investigation of dynamic gas journal and thurst bearings for microturbomachinery

Due to their advantageous characteristics, gas-lubricated bearings are increasingly being adopted in various oil-free applications. These bearings utilize a gas lubricant that is directly sourced from the working fluid of the rotating machine. Furthermore, self-acting bearings eliminate the need for an external supply system or compressor, allowing for the development of compact and hermetically sealed systems. The low viscosity of gaseous lubricants also helps minimize frictional losses, thereby enhancing the overall efficiency of rotating machinery. Another key advantage of gaseous lubricants is their stable physical and chemical properties, as they do not undergo vaporization, cavitation, decomposition, or solidification across a broad temperature range. However, the design of these bearings must be specifically tailored to meet the operational requirements of the system. This thesis presents a study on various types of aerodynamic thrust bearings, aiming to establish performance metrics for the existing bearings, develop accurate numerical models, and propose future improvements to the system. A previously designed test bench was utilized to experimentally evaluate two types of thrust bearings: logarithmic spiral and tapered. Since no prior data were available on their exact geometry, a complete surface scan was performed to characterize the groove pattern and other relevant parameters, ensuring accurate comparisons with the numerical model. The simulation of the system was conducted using a Finite Difference Method (FDM), employing a central node finite volume mesh and a Forward Euler scheme for temporal evolution. While this approach required an exceptionally small time step (dt), leading to long computational times, it was necessary due to the highly coupled nature of the governing equations. The bearings were scanned, and the resulting geometries were directly integrated into the numerical models for validation against the experimental measurements. Both steady-state and time-evolution models were developed and utilized to simulate the system's behavior, providing a comprehensive analysis of aerodynamic thrust bearing performance.