A modal approach to shock buffet lock-in analysis

In a transonic flow, autonomous shock oscillations over rigid aerofoil sections may develop from the interaction between shock waves and intermittently separated shear layers. This unsteady flow phenomenon is exacerbated in an aeroelastic context, wherein large-amplitude structural limit cycle oscillations may evolve from the synchronisation between fluidic and structural modes. Where recent research has employed linear stability analysis to probe the physics of this synchronisation phenomenon, this study investigates the efficacy of the data-driven Hilbert-Huang Transform at extracting physically meaningful information on these underlying modal interactions. The method is found to identify the key characteristics of the pitching response of an aerofoil experiencing shock buffet, with modal interactions that parallel the results of classical stability analysis, albeit with constraints on the breadth of applicability relative to the traditional methods. With this, shock buffet synchronisation is shown to result from an instability in the dominant structural mode.