Particle image velocimetry investigation of flow over unsteady airfoil with trailing edge strip
The flow over a flapped NACA 0012 airfoil, oscillated slightly through the static stall angle, was investigated by using particle image velocimetry, and was supplemented by surface pressure and dynamic load measurements. A significant increase in the dynamic lift force and nose down pitching moment was observed. The most pronounced flow phenomenon was the formation and detachment of an energetic leading edge vortex compared to the no flapped airfoil. The details of the underlying physical mechanisms responsible for the various light stall flow processes were provided via the instantaneous velocity and vorticity fields measurements. In contrast to the Gurney flap, the inverted trailing edge strip led to an improved negative damping while a reduced lift force. The addition of an inverted strip always led to the appearance of a Karman type vortex shedding street immediately downstream of the strip over the entire oscillation cycle.