  Turbine wake and farm blockage effects may significantly impact the power
produced by large wind farms. In this study, we perform Large-Eddy Simulations
(LES) of 50 infinitely large offshore wind farms with different turbine layouts
and wind directions. The LES results are combined with the two-scale momentum
theory (Nishino & Dunstan 2020, J. Fluid Mech. 894, A2) to investigate the
aerodynamic performance of large but finite-sized farms as well. The power of
infinitely large farms is found to be a strong function of the array density,
whereas the power of large finite-sized farms depends on both the array density
and turbine layout. An analytical model derived from the two-scale momentum
theory predicts the impact of array density very well for all 50 farms
investigated and can therefore be used as an upper limit to farm performance.
We also propose a new method to quantify turbine-scale losses (due to
turbine-wake interactions) and farm-scale losses (due to the reduction of
farm-average wind speed). They both depend on the strength of atmospheric
response to the farm, and our results suggest that, for large offshore wind
farms, the farm-scale losses are typically more than twice as large as the
turbine-scale losses. This is found to be due to a two-scale interaction
between turbine wake and farm induction effects, explaining why the impact of
turbine layout on farm power varies with the strength of atmospheric response.
