Initial Investigation of Supercritical Airfoil Dynamic Response due to Transonic Buffet

摘要

On wings of military aircraft, unsteady and complex interactions between the boundary layer and shock wave are commonly encountered. Within localized regions of the flight envelope, this interaction can induce an aeroelastic phenomenon known as transonic buffet. The shock moves periodically due to interaction with the separating boundary layer resulting in a low-frequency high-amplitude load which may pose a serious risk to the health and integrity of the wing. The complexity of identifying the onset of buffet is associated with the dominant turbulent features present, presenting a challenge for eddy-viscosity closure strategies. While there has been significant attention in understanding the aerodynamic mechanisms associated with buffet onset, the dynamic response of the structure and the aeroelastic feedback mechanisms is ultimately more important for accurate quantification of aerodynamic loading responsible for the reduction of fatigue life. This study details the use of Reynolds-Averaged Navier-Stokes (RANS) methods to capture the onset of transonic buffet on the OAT15A supercritical airfoil, and a torsional spring is offered to assess the dynamic structural response of the wing. The study highlights the difference between classical transonic single degree-of-freedom response and bounded limit-cycle-oscillation response characteristic of buffeting systems. This is shown to be dependent on the structural stiffness, affecting the trim position and loading amplitude. The frequency lock-in phenomenon is also observed, and a parametric study is performed to investigate the sensitivity of the system response to the structural natural frequency.