Independent component analysis of non-stationary oscillations due to rotor blade flutter
Collective unstable oscillations of rotor blades in case of flatter are under study. From a linear theory point of view, such unstable oscillations can consist of a single structural mode of blades. It has bee found that flutter of real rotor blades can be two-modal: both torsion and bending mode excites simultaneously. As the collective oscillation amplitude increases, the flutter modes become nonlinear for all rotor blades simultaneously. Nevertheless, as usual, an analysis of respective simultaneous time-series is performed by a linear transform. In present paper it is the Independent component analysis (ICA). The linear ICA transform of multi-dimensional time–series under study displays that, as the rotation frequency increases, the rotor blade flutter evolves through four sequential time-phases: linear torsion flutter, nonlinear torsion flutter with bending mode excitation (torsion-bending flutter), linear bending-torsion flutter with a dominating role of bending mode, and nonlinear bending flutter of an unbounded amplitude increase with time.