Rigid Air Bearings With 3-Lobe Bore Geometry: Stability and Rotor Dynamics for High-Speed Turbosystems

Abstract This paper considers rigid air bearings with a three-lobe bore geometry. They usually exhibit very poor stability characteristics, which make them unsuitable for practical highspeed rotor systems. However, the stability of these bearings may be significantly improved by providing additional external dissipation, which can be achieved by the introduction of damping or friction. Therefore, the bearing shell or ring is not rigidly fixed in the housing but is either viscoelastically mounted to provide external damping, or it can also be elastically mounted by a foil structure to provide dissipation by dry friction. This type of bearing is called an air ring bearing. By properly selecting the bearing and ring supporting parameters, a very stable and robust bearing design can be obtained. This paper analyzes the non-linear vibration behavior and stability of high-speed rotor systems with air ring bearings and discusses the influence of various design and system parameters on the dynamics of the system. Run-up simulations are carried out to investigate rotor oscillations. A detailed co-simulation model is used for this purpose. While the movement of the rotor and rings is described with a multi-body model, the two air films are modeled using two finite element systems.