Influence of Plunge/Pitch Mode on Transonic Buzz Characteristics in Buffeting Flow

Buzz is a critical concern in aeroelasticity in modern aircraft design. It stems from the coupling of flow and structural modes, causing structural instability. As wings grow larger, aeroelastic effects gain more significance, especially the influence of the structural mode of the main wing with higher flexibility on the buzz characteristics. Based on two-dimensional three-degree-of-freedom airfoils, this paper delves into how the plunge and pitch modes affect flap buzz in buffeting flows. Using an aeroelastic model based on a reduced-order model (ROM) and CFD/CSD time-domain simulations, the study shows that airfoil structural modes notably impact flap buzz. The plunge-flap deflection coupling is weak, yet the plunge mode enlarges the instability range of the flap deflection mode. Conversely, the pitch-flap deflection coupling is strong, and the pitch mode shrinks the instability range of the flap deflection mode. Notably, the ratio of flap deflection frequency to plunge frequency has negligible effects on the instability of the flap deflection mode, while the ratio of flap deflection frequency to pitch frequency has significant impacts on it. Adjusting the ratio between the structural frequency and the flap deflection frequency can be an effective strategy for avoiding buzz.