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 flow is turbulent because the tunnel side-wall boundary layer flows over the model, eliminating laminar-turbulent transition from the problem. Without control the flow separates at the highly convex area, and a large turbulent separation bubble is formed at the lee side of the model. Periodic excitation and steady mass transfer were applied to eliminate the separation bubble gradually. During the test, the Reynolds numbers ranged from 7 × 106 to 26 × 106, and the Mach numbers were 0.2 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 angle at low Mach numbers, as in the two-dimensional flow. The conventional swept flow scaling is valid for controlled, fully and even partially attached flow, but different scaling is required for the separated three-dimensional flow. The effectiveness of the active control is not reduced by mild sweep, and the effective frequencies do not change.