Experimental Investigation of an Airfoil Undergoing Large-Amplitude Pitching Motions

摘要

Flow visualization and near-surface hot-wire experiments were performed in the USAF Academy Aeronautics Lab. subsonic wind tunnel on an airfoil undergoing large-amplitude pitching motions about its quarter chord. The experiments were conducted using a NACA 0015 airfoil at an airfoil Reynolds number of 45,000. Two cases are presented in which the angular pitching rate alpha dot is maintained constant during the motion. These two cases represent two different nondimensional pitching rates. Data for the two cases where values of pitching rate are equal to 0.2 and 0.6 show the dramatic effect of pitch rate on flow structure. Large scale vortical structures are seen in both cases at high angles of attack but appear much later and are of a different form for the case with the larger pitching rate value. These structures are very energetic, producing reverse flow velocities near the airfoil surface of 1.0-2.1 times the freestream velocity. (Reprints)