Recovery Control for Rotors Established in Stable Periodic Contact Modes

Previous research has shown that flexible rotors can become established in potentially damaging stable periodic contact modes after initial impact with housings, seals, or auxiliary bearings. These modes are characterized by periodic motion and a fixed contact point in a rotating frame. A contact recovery strategy is developed, with the aim to destabilize the modes and return the rotor to a contact-free orbit. This is achieved by applying compensation forces through magnetic bearings, which reduces the effective synchronous forcing that is causing the contact to a low level. It is shown that even in presence of highly nonlinear contact dynamics, a linear FEM rotor model can be used to calculate appropriate influence coefficients. The contact recovery principle is demonstrated by simulations of a simple disk system and a simple flexible rotor. It is then applied to an experimental flexible rotor test facility. Error margins are investigated, and possible limitations of the method are discussed.