Control of Dynamic Stall Over a Pitching Finite-Aspect-Ratio Wing

摘要

A novel flow control strategy for the delay of unsteady separation and dynamic stall over a pitching finite wing is demonstrated by means of high-fidelity simulations. The control approach relies on very high frequency low-amplitude surface forcing imparted through a zero-net mass flow blowing/suction slot located on the wing lower surface near the leading edge. The flow fields are computed employing an extensively validated high-order large-eddy simulation (LES) approach. The wing of aspect ratio AR = 4 has a NACA 0012 section and a rounded tip. The flow parameters are freestream Mach number M_∞ = 0.1 and chord Reynolds numbers Re_c = 2 × 10~5. A single cycle of an oscillatory pitching motion with nominal reduced frequency k = 0.2 and maximum angle of attack α_(max) = 22° is considered. For the baseline (no control) case the wing experiences deep dynamic stall. Spanwise-uniform pulsed actuation with a primary non-dimensional frequency St; = f_c/U_∞ = 50.0 is capable of maintaining an effectively attached flow during the entire pitching cycle thereby inhibiting the formation of large-scale dynamic stall vortices. Actuation provided a significant reduction in the cycle-averaged drag and in the force and moment fluctuations. In addition, the negative (unstable) net-cycle pitch damping found in the baseline cases was eliminated. Spanwise modulation of the forcing was also investigated including a harmonic variation, as well as a simulated array of segmented actuators.