Abstract: Based on the analysis method of wavelet transformation and incorporated with actuating line model and large eddy simulation, the spatiotemporal evolution of the turbulence structure of wake of a 33 kW horizontal-axis wind turbine was investigated. It was found by the investigation that with the increase of the distance from the rotor rotation plane, the average velocity of wake at each measurement point would decrease first and then gradually increase, the amplitude of the velocity fluctuation would exhibit a decreasing trend; within the region of 7 times of rotor diameter behind the wind turbine, the flow velocity curve would have a pronounced periodicity, reflecting that the passing frequency of the shed vortex was 1.8 Hz, twice as high as the rotation frequency of the wind turbine. The frequency of appearance of blade tip vortices at the measuring point of unit rotor diameter behind the rotor would be from 0.78 to 25.00 Hz, the passing time of the formed vortex tube over the measurement point would be approximately 0.32 s, and the diameter of the vortex tube would be approximately 1.83 m. A low-frequency turbulence structure with frequency from 0.15 to 0.78 Hz would appear at the measuring point of 3-fold rotor diameter from the rotor; the frequency range of blade tip vortex at measuring point of 7-fold rotor diameter from the rotor would be from 1.56 to 25.00 Hz, which was greatly reduced when compared with the case of foregoing blade tip vortex. At the measurement point of 8-fold rotor diameter from the rotor, the vortex tube shape of blade tip vortex similar to that in near wake region would disappear; the blade tip vortex at the measuring point of 9-fold rotor dimeter from the rotor would dissipate almost completely.

Key words: wind turbine wake, turbulence structure, wavelet transform