Some factors affecting stall control with particular emphasis on dynamic stall

Active separation control: an overview of Reynolds and Mach numbers effects

“…Excitation at even higher frequencies (2 F + 11), appears to have very little effect on lift (Fig. 2) [9]. Similar observations have been made in independent investigations [50].…”

“…The data indicated the abrupt nature of separation and attachment, which induced significant C L excursions, up to C L = 0.3, about a mean value of C L = 0.8, while the moment excursions even exceeded their associated mean value. However, hotwire measurements in the upper surface boundary layer at x/c = 0.3 (not shown) did not indicate a preferred shedding frequency [9,12]. It was concluded that a leading-edge bubble-bursting mechanism gave rise to alternating intervals of partial attachment and separation, but with no regular frequency [13].…”

“…Although the mechanism is not understood, these oscillations could be modified by acoustic "tripping". An apparently similar phenomenon just beyond the static stall angle (α = α s + 1 • ) was observed on a NACA 0012 airfoil with an effective leading-edge trip [9,12]. Instantaneous surface pressure measurements were integrated to yield C L and C M time histories (see Figs.…”

“…In contrast to the TAU NACA 0015 baseline configuration, poststall C l and C m unsteadiness was small and, furthermore, the overall effect of excitation was negligible. As pointed out previously, excitation has a small effect on C l and C m oscillations due to the cancellation effect of several vortices simultaneously present on the airfoil surface [9,12].…”

“…Lift increment due to leading edge excitation applied to a post-stalled NACA 0015 airfoil, at different excitation amplitudes (flap not deflected)[9].…”