A large-eddy simulation analysis of collective wind farm axial-induction set points in the presence of blockage

Abstract. Over the past few years, numerous studies have shown the detrimental impact of flow blockage on wind farm power production. In the present work, we investigate the benefits of a simple collective axial-induction set point strategy for power maximization and load reduction in the presence of blockage. To this end, we perform a series of large-eddy simulations (LESs) over a wind farm consisting of 100 IEA 15 MW turbines and build wind farm power and thrust coefficient curves under three different conventionally neutral boundary layers and one truly neutral boundary layer. As a result of the large-scale effects, we show that the wind farm power and thrust coefficient curves deviate significantly from those of an isolated turbine. We carry out a trade-off analysis and determine that, while the optimal thrust set point is still correctly predicted by the Betz limit under wake-only conditions, it shifts towards lower operating regimes under strong blockage conditions. In such cases, we observe a minor power increase with respect to the Betz thrust set point, accompanied by a load reduction of about 5 %. More interestingly, we show that for some conditions the loads can be reduced by up to 19 %, at the expense of a power decrease of only 1 %.