In the unsteady aerodynamics, there are not many studies on the wake parameters of the airfoil. An experimental investigation was carried out to study the unsteady, near wakes behind a wind turbine blade section. Airfoil was made of wood and with 20 cm chord and a span of 50 cm, was given the harmonic plunging motion at range of reduced frequencies, k = 0.03-0.15. The model was oscillated with IUT ALPHA MECHANISM in range of amplitudes ±5mm - ±30mm. To assess the effect of mean incidence, the mean incidence of airfoil was varied at 3 different incidences. 6, 10 and 18 deg. The velocity distribution were calculated from the wake pressure measured by total pressure rake. The time lag of pressure sensors relative to the motion of the trailing edge was exactly measured. Wind tunnel was calibrated before main tests. Turbulence intensity and wind angle was determined with one and two dimensional Hot Wires. To determine the wake displacement, its location was estimated by wake weighted average and for wake deformation, a dimensionless parameter, wake height divided by wake width, was used. Wake displacement was studied in absolute and relative coordinate systems. Results indicate that wake deformation and wake displacement depend on reduced frequency and highly differs between quasi-steady and unsteady oscillations. Reduced frequency produces a great deal on the wake oscillation phase, increasing the frequency reduced the phase difference between the airfoil and the wake but did not affect wake deformation. Also, the experimental results proved that oscillation amplitude affects the wake deformation and increasing the amplitude increases the wake width. Investigations in the relative coordinate system showed that increasing the amplitude makes wake closer to the relative coordinate axis. Keywords: Oscillating Airfoil, Plunging Airfoil, Wake, Reduced Frequency, Wake deformation, Wake Displacement, Total Pressure Rake, Velocity Defect Profile
