Exploiting Low-Strouhal-Number Floating Wind Turbine Platform Motions for Wind Farm Power Improvement

Platform motions of floating offshore wind turbines (FOWTs) are conventionally treated as structural and aerodynamic liabilities to be suppressed through platform and mooring design. This study demonstrates instead that low-Strouhal-number platform motions can potentially be exploited to improve wind farm power output. In a wind-tunnel campaign in the EPFL WiRE atmospheric boundary layer wind tunnel, using WiRE-01 miniature turbines in tandem and an in-house developed three-degree-of-freedom motion platform, we examine four single-axis motions (surge, pitch, sway, and yaw) and two coupled combinations (surge–pitch and sway–roll), over a range of low Strouhal numbers (≤ 0.21) and amplitudes and, for coupled cases, phase differences. Power measurements are combined with particle image velocimetry to link array-level performance to wake characteristics. The tested motions fall into two mechanistically distinct wake-interaction regimes. In the pulsation regime, surge and small-amplitude pitch drive alternating wake expansion and contraction without significantly altering the mean wake, so the downstream rotor remains in the high-deficit core with no net power benefit here. In the displacement regime, sway, yaw, roll, and large-amplitude pitch steer or deflect the wake while enhancing turbulent mixing, exposing the downstream rotor to high-momentum flow and producing consistent gains. For coupled motions, the phase difference governs which regime dominates: in-phase sway–roll coupling maximizes both wake displacement and mixing, achieving the largest measured farm power gain of +15.2%, whereas out-of-phase coupling suppresses both. In-plane motions such as sway and roll also incur substantially lower power fluctuations than out-of-plane motions (e.g., pitch), owing to their limited effect on axial induction, indicating a favorable balance between power gain and grid stability. These findings reveal the potential of low-Strouhal-number FOWT platform motion as an exploitable aerodynamic resource and open a path toward motion-regulation strategies in future floating wind farms.