Combining wake steering and active wake mixing on a large-scale wind farm

Abstract. Wind farm flow control mitigates wake effects within a wind farm by adjusting the turbine settings to improve the overall farm performance rather the output of each turbine. Wake steering is an established approach while active wake mixing has recently emerged as a promising solution. This study quantifies the value of a combined strategy, in which each turbine can apply wake steering or the helix. The analysis is performed considering different degrees of uncertainty in wind direction using engineering wake models which enable the simulation of these techniques on large-scale wind farms. A novel optimization algorithm, called Multi-strategy Serial-Refine (MSR), is developed in this study, extending the state-of-the-art method for yaw optimization to multiple control strategies and a generalized objective. A scaled version of an offshore wind farm in the Netherlands is selected as the case study, consisting of 69 IEA 22 MW turbines. The proposed combined strategy yields a 1.98 % increase in annual energy production compared to the baseline scenario, in contrast to the 1.68 % and 1.15 % gains obtained by applying only wake steering or the helix, respectively. This trend persists under wind direction uncertainty. Given the pronounced sensitivity of wake steering to such uncertainty, the combined strategy takes advantage of the superior robustness of the helix under these circumstances.