Effect of turbine alignment on the average power output of wind-farms

Using Large Eddy Simulation (LES), we investigate the influence of the alignment of successive turbine rows on the average power output of a finite length wind-farm with a stream-wise spacing between the turbines of Sx = 7:85D and a span-wise spacing of Sy = 5:23D, where D is the turbine diameter. Different turbine alignments affect the extent to which wakes from upstream turbines interact with downstream turbines. We consider 13 turbine rows in the stream-wise direction and change the layout of the wind-farm by adjusting the angle y = arctan Sdy Sx with respect to the incoming flow direction, where Sdy indicates the span-wise offset from one turbine row to the next. For the case considered here, y = 0 degrees corresponds to an aligned windfarm, while a perfectly staggered configuration occurs at y =arctan[(5:23D=2)=7:85D]=18:43 degrees. We simulate the interaction between each wind-farm and the atmospheric boundary layer using a LES that uses a newly developed concurrent-precursor inflow method. For an aligned configuration we observe a nearly constant average turbine power output for the second and subsequent turbine rows, which is about 60% of the average power produced by the turbines in the first row. With increasing y the power loss in subsequent turbine rows is more gradual. We find that the highest average power output is not obtained for a staggered wind-farm (y = 18:43 degrees), but for an intermediate alignment of around y = 12 degrees. Such an intermediate alignment allows more turbines to be outside the wake of upstream turbines than in the staggered configuration in which turbines are directly in the wake of turbines placed two rows upstream.