Effects of Sweep on Active Separation Control at High Reynolds Numbers

This paper explores the effects of mild sweep on active separation control at high Reynolds numbers and incompressible Mach numbers. 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-layer e ow is turbulent because the tunnel side-wall boundary layer e ows over the model, eliminating laminar-turbulent transition from the problem. Without control the e ow separates at the highly convex area, and a large turbulent separationbubbleisformedattheleesideofthemodel.Periodicexcitationandsteadymasstransferwereappliedto eliminatetheseparationbubblegradually.During thetest,theReynoldsnumbersrangedfrom 7 £10 6 to26£10 6 , and the Mach numbers were0.2 and 0.25. The test sweep angles were 0 and 30 deg. It was found that the excitation must be introduced slightly upstream of the separation region regardless of the sweep angleat lowMach numbers, as in the two-dimensional e ow. The conventional swept e ow scaling is valid for controlled, fully and even partially attached e ow, but different scaling is required for the separated three-dimensional e ow. The effectiveness of the active control is not reduced by mild sweep, and the effective frequencies do not change.