Layout dependence on spatio-temporal correlations between turbine outputs in large wind plants*

Turbulent boundary layers in which wind turbines operate are characterized by a strong correlation of the velocity field in the streamwise direction. Practically, a significant correlation allows a wind farm controller to use information from upstream turbines to estimate incoming flow conditions for downstream ones. Moreover, the spatio-temporal correlation of the flow is directly linked to the resulting fluctuations of the aggregate wind plant power.  It is evident that the interaction of a turbulent boundary layer with a cluster of large-scale turbines, and their low momentum wakes, is expected to influence the turbulent structure in the wind plant. Here, an existing wind tunnel data-set of a scaled wind farm with sixty instrumented porous disks, and one-hundred models in total (Bossuyt, J. et al. 2017, Exp in Fluids, 58:1), is used to study the effect of layout and wind plant length, on time-lag and correlation of power outputs. The data-set consists of fifty-six different layouts, covering both classical uniform and unconventional non-homogeneous turbine spacings.