FAN NON-SYNCHRONOUS FORCED VIBRATION UNDER CROSSWIND

In this paper, a new aeroelastic phenomena for fans, referred to as Non-Synchronous Forced Vibration (NSFV), is presented. This type of aeroelastic instability can occur at high crosswind conditions when the flow at the intake lip separates and the disturbances caused by flow separation become unsteady. The results show that in presence of unsteady separation in the intake, the fan can experience non-synchronous frequency excitations, which can result in resonant response in modes that are not identified by the Campbell diagram. The findings are corroborated by aeroacoustic theories. To the best knowledge of authors this is the first time that fan forced response due to unsteady distortion is studied and the findings can unlock some of unexplained and unexpected vibrations experienced by engines.