Fan blades of high-bypass-ratio engines, characterized by large size and complex swept-twist geometries, are susceptible to flutter, which poses a severe threat to the safe operation of aircraft engines. Consequently, a comprehensive investigation into aeroelastic stability of fan blades is required to ensure their operational reliability. In this study, the aerodampings of the first vibration mode of the fan blade of a high-bypass-ratio engine at three representative rotational speeds are analyzed using the harmonic balance method and the traveling wave method. The flow fields at the three rotational speeds represent subsonic, transonic, and supersonic flows, respectively. At each speed, the aeroelastic stability of the fan blade is examined from a near-choke condition to a near-stall condition. The results indicate that the aeroelastic stability of the fan blade exhibits distinct trends at different rotational speeds. Specifically, at subsonic and transonic speeds, the aeroelastic stability of the fan blade gradually decreases from the near-choke condition to the near-stall condition, primarily due to an increase in aerodynamic work on the pressure side of the blade. Under the near-stall operating condition at the subsonic speed, the blade exhibits aeroelastic instability in a forward-traveling wave pattern with one nodal diameter. However, at the supersonic speed, the aeroelastic stability initially increases and then decreases with changes in operating conditions. This behavior is attributed to an increase in aerodynamic work in the shock wave region on the suction side of the blade, leading to an aeroelastic instability in a forward-traveling wave with two nodal diameters under the near-stall condition.
Yang et al. (Sat,) studied this question.
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