Computational Assessment of Transonic Airfoil-Gust Aeroelastic Response

This study assesses the aeroelastic response that could arise from a periodic vertical gust of different frequencies encountering an airfoil which consists of a trailing-edge control surface (typically used for transonic aileron-buzz studies) and an airfoil undergoing pitching and plunging aeroelastic motion in transonic flow. The flutter phenomena and limit cycle oscillation correspond to two different types of self-induced instabilities, which happen at a Mach number, freestream velocity, and angle of attack combination for which the airfoil or control surface attains a stable oscillation. Gust acts as an external force to an aerostructural system. The airfoil shows a beating pattern under a periodic gust when the gust frequency coincides with the flutter frequency. However, this pattern evident at flutter velocity is absent when the periodic gust encounters an aeroelastic system at limit cycle oscillation velocity. The present work also shows the impact of periodic gust front on the shock/boundary-layer interaction modifying the coefficient of pressure and coefficient of skin friction distribution and leading to a multiple-frequency and multiple-amplitude aeroelastic motion. Fast Fourier transform is applied to the structural response to explore the frequency content corresponding to the structural response and dominant fluid modes for different flow Mach number regimes under the influence of the periodic gust. These frequency characteristics of the structural responses and flowfield in inviscid and viscous flowfield are distinct for different test cases and reveal the underlying physics of several multiple-frequency and multiple-amplitude aeroelastic motions, frequency coalescence, generation of a new frequency, and so on, as shown in this study.