Compressibility and Excitation Location Effects on High Reynolds Numbers Active Separation Control

The effects of compressibility and excitation slot location on active separation control at high Reynolds numbers are explored. The model, which was tested in a cryogenic pressurized wind tunnel, simulates the upper surface of a 20% thick Glauert–Goldschmied-type airfoil at zero angle of attack. The boundary layers on the model are turbulent because the tunnel sidewall boundary layer flows over it. Without control, the flow separates at the highly convex area of the model and a large turbulent separation bubble is formed. Periodic excitation was applied to control the separation bubble. Two alternative blowing slot locations, as well as the effect of compressibility and steady suction or blowing, were studied. During the test, the chord Reynolds numbers ranged from 1.1 × 107 to 3 × 107 and the Mach numbers ranged from 0.25 to 0.7. It was found that excitation must be introduced slightly upstream of the separation region at low Mach number. Introduction of excitation upstream of the shock wave is more effective than at its foot. Compressibility reduces the ability of steady mass transfer and periodic excitation to control the separation bubble, but periodic excitation has an effect on the integral parameters, which is similar to that observed in low Mach numbers. Blowing becomes more effective than suction at transonic speeds, whereas the opposite was found in low Mach numbers. The data presented provide a proper validation case for unsteady numerical design tool that will enable exploring the full potential of unsteady flow control.