On the Wake/Tailplane Interaction for Established Transonic Airfoil Buffet

Specific upstream flow conditions in transonic flight may incite a highly unsteady flow mode called transonic buffet. The associated periodic shock motion and intermittent separation are transported via the turbulent wake, eventually impinging on aerodynamic components downstream. A generic tandem configuration is investigated in the Trisonic Wind Tunnel of Institute of Aerodynamics (AIA) at M infinity of 0.72, consisting of a main wing (OAT15A) at an angle of attack of 5 degrees and a tailplane (NACA 64A-110) at 0 degrees; chord Reynolds numbers are 2.0x106 and 1.0x106, respectively. Focusing schlieren, particle image velocimetry, and unsteady pressure measurements are conducted to capture the buffet phenomenon, the evolving wake, and its interaction with the tailplane. Temporal and spectral properties of the buffet mode are shown to replicate those of an isolated airfoil but are slightly modified due to a mutual interaction. Periodic shock oscillations at Stc of 0.066 are coupled with intermittent flapping of the wake, which conveys the varying momentum deficit downstream and links both airfoil flow domains. The buffet phase effectively modulates the intensity of emitted vortical structures, imprinting the periodic buffet mode onto the tailplane. Resulting load fluctuations reveal the superposition of a high-frequency unsteadiness attributed to vortex shedding, indicating the greatest receptivity to disturbances around the airfoil suction peak.