Initial Results of an Experimental Study of Oscillating Fence Actuators on a Stationary and Pitch Oscillating Wing

Initial experiments have been conducted to develop methods to characterize ∞ow behavior past stationary and oscillating airfoils for assessment of oscillating fence actuators. In particular, the oscillating fence on a NACA-23012 airfoil has been examined using Particle Image Velocimetry (PIV) and time resolved pressure measurements. Fences and other actuators (eg. synthetic jets) are attractive alternatives to current methods used for ∞utter suppression due to their low power requirement. Such ∞ows are di‐cult because phase averaged measurements require phase locking on both the airfoil position and the fence position (dual phase locking). A bin averaging technique was validated using oscillating fence on stationary airfoil and was successfully implemented as an alternative to dual phase locking for the case of oscillating fence on oscillating airfoil. Pressure measurements over the stationary airfoil with oscillating fence show the formation of a structure with a footprint very similar to that of a vortex whose strength decays rapidly as it convects downstream. Phase locked PIV measurements show formation of two distinct zones, of positive and negative vorticity, as the fence enters the ∞ow. As the fence retracts the structures detach and decay rapidly. Bin averaged pressure distributions for the oscillating airfoil show that pressure ∞uctuations due to the fence appear to be superimposed on that of the baseline oscillating airfoil with no fence. It was also observed that the magnitude of the pressure ∞uctuations due to the fence depend somewhat on the instantaneous airfoil position but depend little on the direction of oscillation (whether increasing or decreasing fi). PIV measurements showed formation, detachment, and decay of the structures is very similar to those for the stationary airfoil, but the structures are comparatively stronger and convect slower.