Dynamic induction control for mitigation of wake-induced power losses: a wind tunnel study under different inflow conditions

Abstract. Dynamic induction control (DIC), also known as the pulse method, is a wake mixing strategy that has shown promising results for mitigating wake-induced power losses in wind farms. It relies on dynamic collective blade pitching to enhance turbulent mixing, thereby accelerating the wake recovery. Experimental validation of this concept has been primarily limited to single-turbine cases under idealised conditions without shear and negligible turbulence. This paper presents a wind tunnel study to investigate the wake recovery improvement induced by DIC in single- and two-turbine configurations, as well as potential power gains in a three-turbine array. The study includes experiments under baseline uniform inflow and two realistic atmospheric boundary layer inflows. Short-range continuous-wave lidar measurements are used to remotely map the time-averaged wake characteristics of each turbine in vertical cross-sections at various downstream positions. First, the wake recovery of the upstream turbine is analysed as a function of pitch amplitude and frequency, with the latter expressed by the dimensionless Strouhal number. Next, the cascading effect of upstream turbine actuation on the wake of a downstream turbine in greedy mode is examined. Finally, wind farm power gains are assessed in a three-turbine setup incorporating a virtual turbine. Compared to the baseline greedy case, improved wake recovery is observed at both the upstream and downstream turbines, solely through upstream turbine actuation across all cases. This improvement is attributed to intensified turbulent mixing driven by DIC, which induces periodic thrust oscillations at both the actively controlled upstream turbine and the passive downstream turbine. The effect is particularly pronounced at higher pitch amplitude, while differences across Strouhal number remain minor, suggesting stronger control authority through increased pitch amplitude. Despite a decrease in DIC-added wake recovery with increasing inflow turbulence, potential power gains for the wind farm persist. Overall, this study demonstrates consistent benefits and adaptability of DIC under realistic inflow conditions, highlighting its greater potential in low-turbulence environments.