The spectral analysis on PIV testing data in Near wake of the wind turbine

The measure on instantaneous velocity field in near wake of horizontal axis wind turbine (HAWT) were carried out using cross correlation particle image velocimetry (PIV) and axis-coder positioning period sampling system at wind tunnel opening. Near wake spectral characteristics were obtained by spectral analysis on PIV testing data at six tip speed ratios. The research result serves as a reference for model updating and numerical simulation of the wind turbine wake. In near wake, the blade passage frequency and its harmonics are the main elements in the axial velocity spectrum, the radial velocity spectrum and the turbulent kinetic energy spectrum. The axial velocity has similar spectral characteristics with the turbulent kinetic energy and has more influence on wake fluctuation than the radial velocity. At rated tip speed ratio, the rotor draws the most energy from wind and has top power coefficient, momentum difference of air pasting the rotor is maximum, so there is the highest fluctuation of the turbulent kinetic energy behind the rotor, at the same time, there is the largest proportion of noise signal in the spectrogram.