Active flow separation control on wall-mounted hump at high Reynolds numbers

An active separation control experiment was conducted in a cryogenic pressurized wind tunnel on a wall-mounted bump at chord Reynolds numbers from 2.4 x 10(6) to 26 x 10(6) and a Mach number of 0.25. The model simulates the upper surface of a 20% thick Glauert-Goldschmied-type airfoil at zero incidence. The turbulent boundary layer of the tunnel sidewall flows over the model and eliminates laminar-turbulent transition from the problem. Indeed, the Reynolds number either based on the chord or boundary-layer thickness had a negligible effect on the flow and its control. Without control, a large turbulent separation bubble is formed at the lee side of the model. Periodic excitation and steady suction or blowing were applied to eliminate gradually the separation bubble. Detailed effects due to variations in the excitation frequency, amplitude, and the steady mass flux are described and compared to those of steady suction or blowing. It was found that the amplitude of the most effective frequency for separation control is rapidly attenuated in the reattachment region. The superposition of weak steady suction enhances the receptivity of the separated shear layer to the fundamental excitation frequency and, therefore, the effectiveness of the periodic excitation, whereas weak steady blowing promotes the generation of higher harmonics and reduces the excitation effectiveness. Separation control using periodic excitation and weak suction are similar in both effectiveness and dynamics, whereas steady blowing generates steadier flow but is of inferior effectiveness and is abrupt in nature and is, therefore, not suitable for closed-loop control. The data set enhances the understanding of active separation control at high Reynolds numbers and is a proper validation case for unsteady numerical design tools.