On the dynamics of windmilling in aero-engines

The relatively new problem of 'windmilling imbalance' in aero-engines is investigated. It falls into the class of rotor/stator rub problems, and thus features many nonlinear effects known from other rub-related phenomena. A simple four-degree-of-freedom model is derived and the results from its analysis compared with measurements conducted on a small-scale test rig. Amplitude jumps and sub- & super-harmonic vibration components were observed. Especially the sub-harmonic components are believed to provide a means to potentially excite the low frequency components of an aircraft, and this needs to be included in the aircraft structural fatigue integrity and cabin environmental assessments.