Experimental analysis of wakes in a utility scale wind farm

Aerodynamics of wind turbine wakes in flat and complex terrains

“…Indeed the scale of the Reynolds number is relevant in physical process such as turbulent mixing, the entrainment of kinetic energy, the evolution and breakdown of tip vortices, etc, all of which are features of wakes in wind farms. The present work extends the authors prior work [15,16] with detailed measurements of the wake up to six diameters in flat and complex terrains. Thus the primary objective of this work is to detail and distinguish the vortex structure and mixing properties of wakes in flat and complex terrains.…”

“…In flat terrain (Fig. 3b), the wind speed and turbulent kinetic energy evolution shows similar characteristic behaviour [16]. The streamwise extent of the near-wake in complex terrain is approximately X/D ¼ 2.…”

“…Alternatively, the turbulent kinetic energy can also be computed from short time Fourier Transform (STFT) as reported earlier [15,16]; both approaches yield the same TKE. In order to quantify the departure from isotropy, the degree of anisotropy (DA) is evaluated as [21].…”

“…The drones are detailed elsewhere [15,16] but some salient characteristics are summarised in Table 2. The seven-sensor fast response aerodynamic probe that is used for wind measurements is described in detail by Mansour et al [17].…”

“…The overall uncertainty of wind speed measurements in Earth's frame of reference obtained from GUM analysis is 0.7 m/s. The approach for computation of wind speed in Earth's frame of reference and the trajectories for measuring in both the near-and far-wake are discussed elsewhere [16,20]. The coordinate system employed here has the wind turbine at the origin (0, 0) facing the upstream wind that flows from the negative X/D axis towards the positive X/D axis.…”