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The passive control of compressible dynamic stall has been experimentally demonstrated in a dynamically oscillating airfoil test at Reynolds numbers near two million and Mach numbers ranging from M = 0.3 to 0.4. A rotorcraft-type airfoil was retrofitted with a leading edge glove, and tested with and without integral molded vortex generators. Even at relatively low free-stream Mach numbers (M = 0.3 to 0.4), the dynamic stall process on the basic airfoil was initiated by a strong shock boundary layer interaction near the airfoil leading edge. When installed on the original airfoil, the vortex generators failed to control leading edge stall as the free-stream Mach number increased from M = 0.3 to 0.4 due to this locally supersonic leading edge flow at high lift. Although not successful in eliminating dynamic stall, the aerodynamic shape of the glove reduced the extent of a supersonic pocket near the leading edge and the subsequent shock strength; as a result, the airfoil retained trailing edge stall behavior during the dynamic stall event. Without the vortex generators, the glove switched the stall from leading edge to trailing edge, but did not alleviate the stall. The combined use of a transonic leading edge glove and vortex generators lead to the alleviation of dynamic stall pitching moments; the two concepts worked together to alleviate the severe pitching moments during stall, even though neither one was successful when used independently. In some light stall cases the adverse pitching moment associated with dynamic stall was completely eliminated up to M = 0.40. For deep stall cases, the adverse pitching moments were alleviated up to a Mach number of M = 0.375, however the method failed for deep stall at M = 0.40 for this configuration.

An active ∞ow control experiment was conducted on a 2-ft chord NACA 0036 airfoil in a 3-ft by 4-ft Wind Tunnel at Re = 1:0 £ 10 6 . The model was equipped with oscillatory jet actuators at x/c = 0.30 and 0.65 that provided 120 Hz periodic excitation at a C„ = 0:86% through 0.06-in wide slots. Three difierent slot conflgurations were tested, including a baseline with no slots. Surface pressure data was collected to compare to previous tests and to combine with turbulence data to aid future CFD modeling efiorts. Turbulence data, measured by hotwire anemometry, was compared with and without ∞ow control. Pressure data corroborates previous test data and provides more points for CFD validation. Hotwire results showed ∞ow control reduced the separated wake size and brought the high Reynolds shear stress layer closer to the airfoil surface. The position of this layer to the surface was altered more signiflcantly than the magnitude of the peak shear stresses. Flow control was shown to increase turbulent energy in the attached boundary layer downstream of the slot but to have little efiect upstream. These results provide further justiflcation to continue assessing the potential of active ∞ow control to reduce separation drag of rotorcraft airframe components.

The objective of this research is mutual validation of computational analysis and experimental measurements of baseline and controlled flow over a blunt configuration. A rectangular wing with a 36 percent thick airfoil was selected as a test case, representing a rotor pylon fairing. However, the results are relevant to thick airfoils in general, and contribute to the study of turbulent boundary layer separation and control. Despite the apparently simple geometry, previous measurements on this NACA 0036 airfoil proved challenging for computational analysis. Computational analysis, using DES, provided accurate prediction of the the massive separation and the effects of the oscillatory flow control. Both the aerodynamic coefficients variation with angle of attack, and the pressure distribution on the wing were in good agreement with measurements. These results stand in contrast to the previous failure of incompressible RANS solutions to reproduce the massive separation, its effect on aerodynamic coefficients, and the impact of flow control from t different slots.