Experimental Analysis of Shock-Acoustic-Wave Interaction in Transonic Flow

The transonic flow around supercritical airfoils is characterized by complex shock-wave/boundary-layer interactions including large-scale self-sustained periodic shock wave oscillations, so-called buffet, which appear at high Mach numbers or incidence angles. The mechanisms behind the buffet phenomenon are not yet fully understood. Since the onset of buffet might seriously deteriorate the overall aerodynamic performance and safety of an airplane wing, gaining further insight to the flow features of buffet is of great industrial interest. The present study targets a deeper understanding of transonic airfoil buffet, in particular, of the acoustic part of the feedback loop, which is supposed to force the shock wave to oscillate. Therefore, the buffet flow field around a supercritical DRA 2303 airfoil model was analyzed by wind tunnel experiments with high-speed (tomographic) particle-image velocimetry and steady and unsteady surface pressure measurements. One focus of the investigations concerns the analysis of the sound emitted at the trailing edge of the airfoil, which forms the acoustic part of the feedback loop. Furthermore, the buffet flow field was manipulated by sound waves of different frequencies and of a varying sound pressure level to study the response of the shock wave movement to an external acoustic forcing.