Alleviation of Airfoil Dynamic Stall Moments via Trailing-Edge-Flap Flow Control

Trailing-edge-flap flow control for the mitigation of large negative pitching moments and negative aerodynamic damping caused by helicopter rotor blade dynamic stall was studied by means of computational fluid dynamics. A discrete vortex method was used for the simulations. The model geometry was a NACA 0012 airfoil oscillating in an α(t )=1 5 deg +1 0deg sin(ω t) motion at the reduced frequency of k = 0.173. The freestream flow conditions were of M = 0.117 and Re = 1.463296 × × 10 6 . The flap actuation was a brief pulse signal of a sinusoidal shape, and it was shown that for optimum results upward flap deflections of the duration of about the 1 of the airfoil motion time period and start time in the third quarter of the azimuth should be applied. Detailed analysis of the flowfield showed that the trailing-edge vortex (TEV), induced by the downstream convecting dynamic stall vortex was in fact responsible for the large negative pitching moments and associated negative damping. The suggested flow control technique displaced the TEV to a higher location, from where its wash down could take place more rapidly. The general applicability of the method was demonstrated on a range of cases pertinent to the helicopter flight envelope.