Modal analysis of transonic shock buffet on 2D airfoil

The paper presents a study of the shock buffet phenomenon on the RA16SC1 supercritical airfoil using the Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) modal approaches. The computational fluid dynamics simulation is validated, and the full buffet envelope of the RA16SC1 airfoil is mapped. POD and DMD techniques are then applied to compute a set of flow modes and corresponding dynamical data (for the DMD method). A dominant buffet mode is identified at the buffet frequency. The corresponding mode shape represents the interaction between the shock wave and boundary layer. Higher modes, at multiples of the buffet frequency, show smaller coherent flow structures at the shock travel area. Further higher modes, of mixed frequencies, are associated with flow structures mainly in the boundary layer area. Only a few modes are required for accurate reconstruction of the buffet flow field. Finally, it is shown that similar modes are present in all buffet angles-of-attack. The modal approach used in this study enables straightforward extraction of the underlying flow structures and dynamic properties of buffet flows.