This paper concerns an experimental investigation of a NACA 0015 airfoil subject to harmonic one-degree-of-freedom translatory motion. Specifically, unsteady pressure distributions were measured at a range of incidences and movement directions at reduced frequencies matching real life conditions for the lead-lag motion of wind turbine rotors. From the experimental results, hysteresis loops and aerodynamic damping were computed and compared to results from linear quasi-stationary theory and unsteady potential flow theory. The maximum negative aerodynamic damping was found to take place at moderate stall and an incidence of about 15°, at a movement direction close to the chordwise direction. Comparison with unsteady potential flow theory showed excellent agreement with the experimental data for incidences up to 5°. Linear quasi-stationary theory failed to reproduce the overall features of the aerodynamic damping for incidences above 12°.

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