Aeroelastic stability of elastic skin of airfoil in transonic buffeting flow

Abstract

Transonic buffeting is a large self-oscillation phenomenon of shock waves caused by shock wave–boundary layer interference. The thin and light structure of an aircraft, such as its elastic skin, is easily coupled with the transonic separation flow, thus inducing complex aeroelastic problems. In this study, we conducted an aeroelastic stability analysis of the local elastic skin of the airfoil in transonic flow based on the time domain simulation method and the reduced-order model. We established an aeroelastic reduced-order model of the local elastic skin, predicted the skin instability boundary, and analyzed its coupling mechanism. We found that the single-degree-of-freedom flutter phenomenon of the skin occurred only when the natural frequency of the skin was lower than the flow frequency. Increasing the structural frequency of the elastic skin was beneficial to improving the stability of the skin's aeroelastic system. In the subcritical state of buffeting, the near-instability flow mode induced structural modal instability, causing single-degree-of-freedom buffeting of the skin. In the buffeting supercritical state, the skin aeroelastic system exhibited a “lock-in” phenomenon, that is, the system response frequency was locked to the structural frequency. This single-degree-of-freedom flutter phenomenon was essentially caused by unstable flow modes inducing structural mode instability. Skin flutter changed the shock-wave motion period and affected the position of the separation vortex. When the natural frequency of the wing skin was close to the flow frequency, the system became unstable and was accompanied by an interaction of buffet and flutter, which ultimately manifested as limit cycle oscillations (LCOs).