Experimental Aeroelastic Response for a Freeplay Control Surface in Buffeting Flow

A partial control surface is constructed near the midspan of a NACA 0012 airfoil model with and without freeplay gaps. Static and dynamic control surface pitch motion measurements were performed in wind-tunnel tests at higher angles of attack including buffet or von Karman vortex street flows. Two typical angles of attack, alpha = 20 and 40 deg, and four freplay gaps in the pitch stiffness, delta = 0.25, 0.5, 0.75, and 1.0 deg, are considered in the tests. This study has measured the static and dynamic responses of the flap pitch motion (with and without freeplay gaps) induced by the buffeting flow. Also, the buffeting frequency has been determined from the measured flap pitch responses. The buffet flow occurs at large angles of attack, and this leads to a larger preload from the aerodynamic forces and a larger static pitch equilibrium position. In this case, there is no limit cycle oscillations of the flap pitch motion induced by the freeplay gap to be found. Because the flap pitch motions are around the upper boundary of the freeplay gap, the dynamic pitch response has only a small change with different freeplay gaps. Buffeting flow excitation leads to a large dynamic response when the buffeting frequency is close to the flap natural frequency.