Oscillating Wing Loadings with Trailing-Edge Strips

Abstract

The dynamic-load loops of an oscillating NACA 0012 airfoil, obtained from surface-pressure measurements, fitted with small full-span trailing-edge strips, positioned on the lower (i.e., the Gurney flaps) and/or upper (the inverted strips) surface at the wing trailing edge, of height of 1.6 and 3.2% of the airfoil chord were studied at Re = 1.07 x 105. The results show that, similar to a static wing, the Gurney flap concept was also fairly generally applicable, in terms of lift performance enhancement, to an oscillating airfoil, despite the large and small increases in the peak negative pitching moment and maximum drag force, respectively, as well as a promoted dynamic stall. The increase (decrease) in the nose-down pitching moment (dynamic-stall angle) can be alleviated by the use of inverted strips at the price of a reduced maximum lift coefficient. The asymmetric strips were found to provide a compromise in the dynamic aerodynamic performance between the regular and inverted Gurney flaps, including a 49-deg flap, of an oscillating airfoil. The present passive oscillating-wing C 1 -C d -C m control can be valuable, because it can be used as an experimental guideline for the active control of the dynamic stall and/or nose-down pitching moment via a spanwise trailing-edge flap.