Qualitative and quantitative description of a wind turbine wake

Wind tunnel experimental data from the wake of a model wind turbine was used to provide a scale by scale energetic description of the the flow at different vertical and downwind locations. Premultiplied spectra of the streamwise and vertical velocity component were considered for the analysis and compared with those obtained in smooth wall conditions (base flow). Results showed that in the relatively high frequency range, the turbine induces strong turbulent energy into the wake, which is an indicator of its active character. However large scales and very large scales were observed to be dampened in the wake close to the wall. These two distinct processes occurring in the wake suggest to conceptualize and model the turbine as an active filter. The dominant terms in the turbulent kinetic energy (TKE) equation were also estimated at different locations to study the physical proceses modulating the enhanced levels of turbulence intensity observed in the wake of wind turbines. The ratio between the cube of the u-rms at hub height and the rotor diameter showed to be a reasonable scaling quantity for TKE production and dissipation.