Early Warning Signal Based on Global Dynamics for Instability Responses in Rotor/Stator Rubbing System

In a rotor system with a tiny clearance between blade and stator, the undesired dry friction backward whirl may be suddenly aroused by the global bifurcation to cause a destructive response up to clearance tens of times. To detect in advance the resulting sharp increase in amplitude, the evolution of Poincaré return points of response time-series is proposed as an index of stability in this paper to identify if the dangerous bifurcation happen. The uptrend of the proposed index in the Poincaré space indicates the change of response stability. Focusing on a disturbed rotor-rubbing system, the global dynamics before dry friction backward whirl occurs is investigated to reveal the mechanism of the proposed early warning signal. By setting multi-level warning thresholds, the signal can work nicely prior to rubbing happen when the dry friction backward whirl is coming on to avoid irreparable accidents as much as possible.