On the effect of varying momentum coefficient on separation control for a thick symmetric airfoil

This study examined flow separation control on a National Advisory Committee for Aeronautics 0025 airfoil through an array of microblowers, systematically analyzing the effects of momentum coefficient (Cμ) at a chord-based Reynolds number of Rec=100 000 and 10° angle of attack. Surface pressure measurements and particle image velocimetry characterized the lift recovery and flow dynamics across different forcing frequencies (F+) and locations (xj/c) over a range of momentum coefficients. Results revealed that lower reduced frequencies (F+∼1) required a lower momentum coefficient threshold for effective flow control than higher frequencies (F+∼10). Progressively increasing Cμ systematically energized Kelvin–Helmholtz waves within the separated shear layer, with wave structures critically dependent on the forcing frequency. These energized vortices enhanced momentum transfer from the freestream, facilitating reattachment of the separated shear layer to the airfoil surface. Beyond initial reattachment, further increases in momentum coefficient produced frequency-specific modifications to the attached flow characteristics.