Model-Free Control Methods for Recovery from Touchdowns Involving Circular Whirl

In this paper, the dynamics associated with rotor-stator touchdowns involving full circular rub are considered. The expected range of phase shifts occurring in various measurable signals are examined from a theoretical standpoint, with the aim of developing model-free control algorithms that can recover contact-free rotor levitation from a state involving persistent rub with touchdown bearings. Two different strategies are proposed, according to whether touchdowns planes can be considered collocated with the AMBs or not. Requirements for successful operation, in terms of available sub-models and measurement information, as well as possible deficiencies are explained and verified through experimental tests on a multi-mode flexible rotor test rig.