Unsteady wave phenomena on a supercritical airfoil

Transonic flow investigations are performed in a modified shock tube with a rectangular test section. The investigated model is a BAC3-11 airfoil with a constant cord length and a sharp trailing edge. Time-resolved shadowgraphs and schlieren pictures show pressure waves initiated near the trailing edge and propagating upstream, where they become apparently weaker near the leading edge. These wave processes are accompanied by wake fluctuations and vortex generation in the boundary layer. The observed waves are also captured by pressure transducers mounted in the airfoil model. The dominant frequencies range between approximately 0.7 and 1.5 kHz. Using statistical analysis of the pressure histories, wave propagation direction and wave speed are determined. For higher flow Mach numbers, a strong wave/shock interaction is also observed in which the shock, depending on the shock strength, is attenuated and degenerated into compression waves.