Airfoil Unsteady Aeroelastic Responses in Buffeting Transonic Flows

Abstract

buffeting flow were conducted using Navier-Stokes turbulent CFD solver. The buffeting flow exhibits shock wave oscillations of a unique frequency. The elastic system was assigned with natural frequencies ranging from below to above the buffet frequency, and with various mass ratios and damping values. Numerical simulations of the aeroelastic system reveal three distinct response characteristics, depending on the relationship of the system’s natural frequency to the buffet frequency, and on the system’s mass ratio. Elastic systems with natural frequencies that are lower than the buffet frequency exhibit a single-frequency response, with a frequency that is shifted form the buffet frequency towards the elastic natural frequency as the mass ratio is decreased (and the magnitude of the elastic response increases). Elastic system with a natural frequency that is the same as the buffet frequency exhibits resonance. Elastic systems with natural frequencies that are higher than the buffet frequency exhibit a response with two distinct frequencies, that of the buffet and that of the elastic natural frequency. As long as the pitch amplitudes are small, the response is mostly at the buffet frequency. As the pitch amplitudes increase there is more power in the elastic natural frequency, and less in the buffet frequency. As the pitch amplitudes further grow, the response is in the elastic natural frequency solely, and the buffet frequency vanishes. This behavior agrees with the lock-in phenomenon that was previously observed in the case of prescribed airfoil motions. This aeroelastic behavior may be responsible for limit cycle oscillation and torsional buzz phenomena that are observed in wind tunnel tests at the transonic flight regime.