Analysis of Air Foil Thrust Bearings Under Misalignment Conditions Featuring Performance Limit Curves

Abstract This article explores the performance of foil thrust bearings under misalignment conditions, highlighting the need for a fully coupled simulation model to capture their thermo-mechanical behavior. The in-depth multiphysical nonlinear finite element model used here calculates foil and rotor disk deformations and temperatures as well as the film pressure and temperature. Misalignment causes each bearing pad to have unique height functions, pressure loads, and power losses, making single-pad analysis insufficient. The proposed model consists of a rotor with a multipad air foil thrust bearing, accurately representing misaligned configurations. Frequently, performance maps are used to show the relationship between thrust load and power loss of the thrust bearing. The main finding of this work lies in the proof of the existence of two characteristic performance limit curves for air foil thrust bearings, which limit the possible performance area. Bearing operation without misalignment marks the limit curve with the lowest losses, while the other limit curve is generated at increasing misalignment angles while maintaining the lowest allowable gap height to avoid mixed lubrication conditions. The here presented two limit curves may be of high practical interest since they define the operation boundaries of the thrust bearing and describe possible operation points for arbitrary misalignment configurations. For the case without misalignment, classical 1D performance lines are sufficient. However, if misalignment is considered, the bearing performance has to be described by 2D performance areas.