Comparison of wind-farm control strategies under realistic offshore wind conditions: turbine quantities of interest

Abstract. Wind farm control is a strategy to increase the efficiency, and therefore lower the levelized cost of energy, a wind farm. This is done by using turbine settings such as the yaw angle, blade pitch angles, or generator torque to manipulate the wake behind the turbine affecting downstream turbines in the farm. Two inherently different wind farm control methods have been identified in literature: wake steering and wake mixing. This paper focuses on comparing the turbine quantities of interest between these methods for a simple two-turbine wind farm setup, while a companion article (Brown et al., 2025) focuses on the wake quantities of interest for a single wind turbine setup. Both papers use the same set of wind farm simulations based on high-fidelity large-eddy simulations (LES) coupled with OpenFAST turbine models. First, precursor simulations are executed in order to match wind conditions measured with lidars in an offshore wind farm off the US east coast. These measurements indicate general wind conditions that exhibit substantially higher vertical wind shear and veer than any of the LES studies performed with wind farm control strategies currently available in literature. The precursors are used to evaluate the effectiveness of the control methods. In the LES simulations, the wind veer leads to highly skewed wakes, which has considerable influence on the power uplift of wind farm control strategies. In addition to a baseline controller, four different control strategies, each of which uses either pitch or yaw control, are implemented on the upstream turbine of a simple two-turbine wind farm. Assuming the wind direction is known and constant over time, the simulations show that wake steering is generally the superior wind farm control strategy considering both wind farm power production and turbine damage equivalent loads (DELs) when substantial wind veer is present. This result is consistent over different wind speeds and wind directions. On the other hand, for similar wind conditions with lower veer, wake mixing was found to yield the highest power production, although at the expense of generally higher loads. This leads us to conclude that the effect of wind veer, which was so far not usually considered, can not be neglected when determining the optimal wind farm control strategy.