Leading-Edge Flow Structure of a Dynamically Pitching NACA 0012 Airfoil
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The leading edge flow structure of the NACA 0012 airfoil is experimentally investigated under dynamic stall conditions (M = 0.1, = 16.7 Rec = 1106 where c is the chord) using planar particle image velocimetry. The airfoil was dynamically pitched about the 1/4 chord at a reduced frequency, k = 0.1. As expected, under dynamical pitching conditions the flow remains attached in the leading edge region above the static stall angle, whereas during downstroke, the flow remains separated below the static stall angle. A phase averaging procedure involving triple velocity decomposition in combination with the Hilbert transform enables the entire dynamical stall process to be visualized in a novel coordinate system, with the added benefit of visualizing multiple cycles as multi-phase cycles. The genesis of the leading edge vortex is observed, which is seen to grow, bifurcate into two distinct vortices, and then convect downstream. 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.