Backup Bearing Modelling for Turbo Machines with High Axial and Radial Loads

The use of active magnetic bearings (AMBs) in turbo machines is an active research topic and the implementation in industrial applications is becoming commonplace. This is especially true when investigating the backup bearings (BBs) for high speed rotors with high axial and radial loads. In AMB supported turbo machines there usually are high axial process forces present, and should the axial AMB (AAMB) fail, these forces need to be supported by the axial backup bearings (ABBs). In order to design appropriate BBs the movement of the rotor and the associated forces produced during a rotor delevitation event (RDE) is of critical importance. These forces should be determined using a rotor delevitation model that includes the forces on all the backup bearings and the effect that these forces have on the rotor stability. This paper presents a short overview of various types of ABBs in the literature and the associated models for these BBs. The second part of the paper presents a model for a novel BB currently under construction at the IPM, and how this model is integrated into the rotor delevitation model BBSim [1]. The third part of the paper presents some results obtained using the proposed ABB model. The results investigate the effect that the radial distance where contact occurs and the axial force present on the rotor has on the RDE severity based on the Vval values.