Effects of Wake Interaction on Downstream Wind Turbines

The present article revisits the wake studies behind the NREL (National Renewable Energy Laboratory) Phase VI wind turbine inside a virtual wind tunnel that were recently performed at the University of Adelaide using Large Eddy Simulation (LES). A notable observation has been made in the current article, through comparisons of instantaneous contours of vorticity, velocity and turbulence intensity, that the regions of velocity deficits and high turbulence intensities in the wake are restricted to the regions of high vorticity. Therefore, for a downstream wind turbine, the smaller power production, the increased unsteady loads and the noise produced can directly be associated with the turbine blades passing through the streamwise vortices generated by the upstream wind turbine. In addition, a comparative analysis has been performed between the LES and semi-empirical models, used in the industry, to better understand the development of the wake inside the wind tunnel model. Finally, in order to illustrate the effects of wake on downstream wind turbines, a dynamic stall prediction model was used to determine the regions of the turbine blade affected by dynamic stall as a function of spacing between the turbines.