A large-eddy simulation analysis of collective wind-farm axial-induction control 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 control strategy on power maximization and load reduction in the presence of blockage. To this end, we perform a series of large-eddy simulations (LES) over a wind-farm consisting of 100 IEA 15MW turbines, and build the wind-farm power and thrust coefficient curves for three different conventionally neutral boundary layer profiles. We show that the wind-farm power and thrust coefficient curves are much flatter than those of an isolated turbine. As a result, the wind-farm thrust coefficient becomes significantly more sensitive to the selected operating point than the power coefficient. Consequently, we find that the optimal wind-farm operating point considerably differs from the Betz limit in practice, particularly under high-blockage conditions. At the optimal point, the results reveal a minor power increase, accompanied by a load reduction of about 5 %, simultaneously. More interestingly, we show that in some cases the loads can be reduced by up to 19 %, at the expense of a power decrease of only 1 %.