CFD-based investigation of lubrication flow and thermal behaviour in high-speed turbomachinery bearings

Abstract

In this thesis, Computational Fluid Dynamics (CFD) is used to study the flow of lubricant within the ball bearings of high-speed turbocharger. The performance of ball bearings within high-speed turbomachinery is essential to the reliability of the machine, yet the methods that are often used to study their behavior within such conditions can be limited. Consequently, a CFD model was created within ANSYS Fluent to simulate the fluid dynamics within a turbocharger bearing cartridge. Both the steady-state (MRF) and transient (Sliding Mesh) methods were utilized within the software to create this model, which included features related to turbulence, heat transfer, and the geometry of the bearings.

The results of the simulation indicated that the flow within the bearings was turbulent, with high velocities within the rotating components of the bearing, yet low pressures within those same areas, indicating the potential for cavitation within the bearing. Additionally, maps of the temperature of the fluid within the bearing indicated the convective heat transfer from the bearing components lubricant - coolant. Each type of simulation resulted in similar trends within the same parameters, yet the Sliding Mesh model better represented the transient behavior of the lubricant.

Though limited in its current state to a two-dimensional model of the bearing with single-phase fluid motion, the created model provides a means of analyzing the behavior of ball bearings within high-speed turbomachinery.