Control of a Laminar Separation Bubble on a NACA 0009 Airfoil Using Electroactive Polymers

Control of a laminar separation bubble on a two-dimensional NACA 0009 was investigated experimentally in an open-return wind tunnel using particle image velocimetry measurements at a range of chord-based Reynolds numbers ReC between 2.0 • 104 and 3.0 • 104. In this study, flow control was accomplished through a row of surfacemounted electroactive polymers, centered at 20% of the airfoil chord. A three-dimensional separation bubble was seen to exist when the airfoil's angle of attack was set at 5 deg, in agreement with the literature. Furthermore, the streamwise and cross-stream extents of the bubble decrease with the increase of the Reynolds number. To mitigate the separation bubble, the electroactive polymers were actuated at a frequency corresponding to the Kelvin-Helmholtz instability of the separated mixing layer. This frequency was found by applying the solution to the Michalke spatial stability analysis to the experimental data. Activation of the electroactive polymers resulted in mitigation of the separation bubble, as evidenced from suppression of reverse flow within the near-surface velocity profiles.