Coupled Airfoil Heave/Pitch Oscillations at Buffet Flow

The influence of coupled heave and pitch oscillations on the transonic flowfield over a supercritical DRA 2303 laminar-type airfoil in buffet conditions is analyzed using a combination of time-resolved stereo particle-image velocimetry and unsteady pressure measurements. Three flow configurations at a Mach number of and at an angle of attack of are analyzed to show the impact of the fluid-structure interaction on the overall flow structure: the flow over a fixed DRA 2303, the flow over a DRA 2303 undergoing flow-induced motion, and the flow over a DRA 2303 experiencing a forced sinusoidal heave/pitch motion at frequencies in the range of the natural buffet frequency of the airfoil. The results are analyzed regarding the origin and nature of the unsteady shock-boundary-layer interaction, the fluid-structure response behavior, and the influence of the structural motion on the shock oscillation. For the buffet flow, the shock motion is determined by the sound pressure level generated at the trailing edge. At buffet conditions, the frequency of the self-sustained airfoil motion is in the same range as the natural buffet frequency. At forced oscillation at excitation frequencies in the buffet range, the shock oscillation locks into the excitation frequency indeed, but the sound-wave-based feedback loop is hardly influenced by the airfoil motion.