Reduction of subsynchronous vibrations in a single-disk rotor using an active magnetic damper

Rotor instabilities in turbomachinery often manifest themselves as a re-excitation of the first rotor critical speed resulting in lateral rotor vibrations at a frequency below the rotor operating frequency. Considerable work exists in the literature involving the analysis of destabilizing mechanisms and passive solutions for reducing subsynchronous vibrations. The authors propose here a novel active control solution utilizing active magnetic bearing (AMB) technology in conjunction with conventional support bearings. The AMB is utilized as an active magnetic damper (AMD) at rotor locations inboard of conventional support bearings. Presented here are initial proof-of-concept experimental results using an AMD for vibration control of subsynchronous rotor vibrations in a high-speed single-disk laboratory rotor. The study shows that subsynchronous vibrations are reducible with an AMD and up to a 93% reduction in the amplitude of subsynchronous vibrations is demonstrated. The study also shows that the AMD can significantly increase synchronous vibration response (up to 218% in one case) by increasing system stiffness and pushing a critical speed closer to an operating speed. The overall results from this work demonstrate that reduction in subsynchronous response is feasible and that full rotor dynamic analysis and design is critical for the successful application of this approach.