Forced and Aeroelastic Responses of Bird-Damaged Fan Blades: A Comparison and Its Implications

The aeroelastic response of a bird-damaged fan stage at the inlet of a high-bypass ratio turbofan engine is examined using a combined computational fluid dynamics and computational structural dynamics framework. The damaged fan sector consists of five blades obtained from accurate numerical simulation of the bird impact. Forced and aeroelastic response calculations are performed and compared to assess the role of aeroelastic coupling. The calculations are performed at 100, 75, and 60% throttle settings to investigate the role of engine speed on the fan response. Results from the forced response and aeroelastic response calculations indicate that the undamaged blades opposite the damaged sector exhibit the highest level of structural response. Comparing the forced response with the aeroelastic response shows increased participation of the higher structural modes, especially for the damaged blades, that grow in time or exhibit beating. Examination of the work performed by the aerodynamic forces suggests that the growth in blade response is due to aeroelastic phenomena and can cause a potential instability. The results illustrate the importance of aeroelastic effects when predicting the post-bird-strike fan response.