Full-size rotordynamic test rig for magnetic and auxiliary bearing testing and initial results

Recent challenges in turbocompresor design include applications in subsea installations as well as remote operation in unmanned floating platforms. These applications benefit from oil-free operation which solves technical hurdles while being environmentally friendly. The most mature oil-free rotor support technology today is the magnetic bearing which is being used by several manufacturers as their standard solution to these advanced applications. These systems require auxiliary bearings to contain the rotor in case of a power failure to the magnetic bearings or a transient event. In general, there exists the need to develop commercial solutions for auxiliary bearings to extend its life, in particular regarding cumulative damage associated to drop events. This paper presents the design of a configurable test rig that can accommodate different rotor sizes, up to 1200 mm in bearing span, and 711 mm diameter wheels. The rig can also accommodate bearing sizes up to 229 mm. Rig pedestals can fit different bearing types such as magnetic bearings and/or auxiliary bearings independently, including oil bearings for comparison purposes. Misalignment and support flexibility effects are also possible. A 15.5 kW, variable speed electric motor drives the test rotor up to a speed limit of 10,000 rpm. Initial experiments on auxiliary bearings are shown for a 5- impeller, 57.8 kg, subcritical compressor rotor without drop events to study the baseline dynamic behavior of roller-element bearings (with inner clearance) on soft supports (o-rings). These experiments are presented to illustrate non-linear vibration regimes present during rotor-stator interaction with a highly unbalanced rotor. Experimental evidence presented can be used to fine-tune current auxiliary bearing models to improve rotordynamic predictive codes.