A study of separation on airfoils undergoing pitch, surge and combined motions
Vertical axis wind turbine blades undergo a large angle of attack and velocity variation during every turbine rotation. The flow over a NACA 0018 airfoil undergoing sinusoidal pitch, surge and combined motions at similar frequency, amplitude and Reynolds number as a commercial turbine was measured to investigate the effect of the different motions on the flow field. Two-dimensional, time resolved velocity fields were acquired using particle image velocimetry. Vorticity contours of the phase-averaged flow were used to visualize the separation process and shear layer development. The pitch-only ease is seen to separate earlier and at a lower angle of attack than the combined case. Results for surging airfoils at two angles of attack are presented, one fully separated, and one partially separated. Surge forward is shown to move the separation point toward the leading edge, while surge back moved it aft. The dynamics of the leading edge vortex in the combined pitch/surge and pitch motions are discussed.
© 2015 American Institute of Aeronautics and Astronautics. Published Online: 19 Jun 2015.