Evaluation and Analysis of Different Hydrostatic Bearing Designs Inside an Electrical Machine

Abstract

This report is a part of a master’s thesis on evaluation and analysis of different hydrostatic fluid bearing designs which are employed inside an electrical machine. The evaluation is made numerically using Simcenter STAR-CCM+ (STAR-CCM+). A CAD model of the currently used fluid bearing design is provided which is then modified into different geometries, focusing on the recess pocket’s shape and the fluid film thickness. The CAD models are imported into STAR-CCM+ and meshed taking the fundamentals of fluid mechanics, turbulence modelling and computational fluid dynamics into account. An unstructured trimmed cell mesher together with a prism layer mesher are used to mesh the domain. The fluid simulation was solved as a steady state incompressible liquid with mostly standardized settings. For the turbulence closure model the k-ω is used to provide a better solution in the viscous sublayer for better accuracy regarding the wall shear stress on the rotor. Appropriate boundary conditions are set up for the moving and stationary walls as well as for the inlets, outlets, symmetry planes, and interfaces for the periodicity.

Fluid simulations have been performed for a number of different geometries. A comparison between the different geometries’ performance regarding maximum and minimum pressure, power consumption, risk of cavitation, and pressure distribution is made where it can be seen that the differences between the geometries are small. A comparison is also made for when the fluid film thickness over the lands increases or decreases linearly with an increasing radial coordinate. It can be seen that the difference between the simulated geometries in this case is more substantial, where a noticeable difference in the pressure distribution between the geometries can be seen but both configurations show a risk for cavitation. The conclusion from the calculations is that the pocket shape does not affect the power consumption in a significant way, although the size of the pockets influences the viscous friction losses and more shallow pockets display higher maximum pressures. Also, the calculations show that there is a risk of cavitation if the fluid bearing is unbalanced due to unbalanced magnetic forces.