Investigation of Multiblade Wind-Turbine Wakes in Turbulent Boundary Layer

A wind tunnel experiment was carried out to investigate the complicated turbulence characteristics of wakes produced from two-blade, three-blade, and four-blade miniature wind turbines operating in a neutrally stratified turbulent boundary layer. A calibration-free Cobra probe was adopted to measure the streamwise, spanwise, and vertical components of the instantaneous wind velocity in the turbine wakes. A noncontact laser tachometer was used to measure the blade rotation speed. Key turbulence statistics including mean velocity, turbulence intensity, momentum flux, and power spectrum were analyzed. The measured results show that the four-blade turbine produced smaller streamwise velocity, accompanied by stronger enhancement of turbulence intensity and vertical momentum flux, in the near-wake region at a distance of 6 rotor diameters downstream of the turbine. In the further downstream wake region, the velocity deficits behind the turbines were relatively consistent in the wake location after 8 rotor diameters, which indicates that wake recovery had the same extent whether the wakes were produced from the two-, three-, or four-blade wind turbines. Energy spectrum analysis of the instantaneous streamwise velocity had a slope of -5/3 within the turbulence inertial subrange to increase the reliability of the wind speed data collected using the Cobra probe. (C) 2019 American Society of Civil Engineers.