Experimental comparison of a NACA0021 airfoil in large plunging and surging motions at 90 °angle of attack
G. Xu (TU Delft - Wind Energy)
W. Yu (TU Delft - Wind Energy)
Carlos Simao Ferreira (TU Delft - Wind Energy)
Andrea Sciacchitano (TU Delft - Aerodynamics)
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Abstract
The topic of vortex-induced vibrations on a wind turbine blade has recently gained much attention due to its growing size and flexibility. To address this concern, a wind tunnel test was conducted to study the forced plunging and surging motion of a NACA0021 airfoil at 90° angle of attack. Results indicate that vortex lock-in occurred for a motion amplitude of one chord length even for a small frequency ratio (between motion frequency and static Strouhal frequency) of 0.39. Analysis of the drag coefficient, derived from the phase-averaged Particle Image Velocimetry (PIV) data, shows that a plunging airfoil experiences higher average loading than a surging airfoil, which is deemed to be more harmful considering the higher loading in the crossflow-direction due to the variation of effective angle of attack.
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