Spatial study of the wake meandering using modelled wind turbines in a wind tunnel

Abstract

The present paper presents a study of the wake meandering phenomenon with the help of physical modelling in atmospheric boundary layer (ABL) wind tunnel. The wind turbine is modelled at a geometric scale of 1:400 with a static porous disk (actuator disk concept). The main objective of the present work was to supply quantitative information on the meandering process. The instantaneous wake width and its horizontal and vertical swerves from the mean wake axis are quantified using specific image processing of instantaneous velocity fields obtained by particle image velocimetry downstream of the modelled wind turbine. We observe that the wind turbine wake displacements from the mean streamwise axis are very important when the turbulence length scales are larger than the wake width. We also observe that, in ABL conditions, horizontal displacements are higher than the vertical ones with a proportion in agreement with the ratio between the transverse and vertical turbulence intensities δ vδω ≈ 3/2. It is finally concluded that the instantaneous wake width remained nearly constant downstream of the wind turbine model whatever the flow conditions and that the extent of the mean wind turbine wake is dominantly due to the meandering process. This confirms that it is necessary to include the meandering process in the wake analysis in order to estimate the fatigue loading on wind turbines within wind farms properly. © 2011 John Wiley & Sons, Ltd.