Floating wind turbines have a hidden wake behavior that could reshape how offshore wind farms are designed
Floating wind turbines don’t just spin — they sway, surge, and rock with the ocean beneath them. Engineers have long treated that motion as an aerodynamic nuisance, something to design around rather than learn from.
When researchers at the University of Oldenburg pushed a model turbine through surge frequencies well beyond anything previously tested, they expected the wake to stay indifferent. Instead, they found something never before documented: at certain surge frequencies near the blade passing frequency, the turbine’s oscillating motion couples with rotor rotation to generate a coherent wake structure — one that dramatically accelerates wind recovery far downstream.
Why floating turbines move — and why it matters for wind farms
Floating offshore wind turbines don’t sit on fixed foundations. Anchored by moorings, they respond continuously to wind loads and ocean waves, experiencing surge, sway, and pitch motions across a wide range of frequencies and amplitudes — and those motions directly alter how the rotor interacts with surrounding air.
Four parameters were varied independently: motion frequency (Stp), normalized velocity amplitude (ΔV*), tip speed ratio (TSR), and thrust coefficient (CT).
Behind every turbine lies a wake: a corridor of slower, more turbulent air stretching many rotor diameters downstream. When the next turbine sits inside that wake, it captures less energy. Faster wake recovery translates directly into higher output for the whole array.
Prior research found that low-frequency surge motions can help stir the wake and speed recovery. The higher-frequency end of the motion spectrum remained largely uncharted — and that gap turned out to matter more than expected.
An experiment designed to push beyond known limits
Researchers at the University of Oldenburg mounted a two-bladed model turbine on a linear actuator capable of producing surge motions at frequencies up to 22.6 Hz, reaching platform Strouhal numbers (Stp) as high as 7 — more than three times beyond what previous experimental studies had tested.
Four parameters were varied independently: motion frequency (Stp), normalized velocity amplitude (ΔV*), tip speed ratio (TSR), and thrust coefficient (CT). Earlier studies had often changed multiple conditions simultaneously, making it hard to isolate which factor actually drove wake recovery changes.
Tests ran under near-laminar inflow — turbulence intensity of 0.3% — and turbulent conditions generated by an active grid, reaching turbulence intensities up to 4.7%. The laminar baseline isolated the motion’s effect cleanly, while turbulent cases tested whether findings held under more realistic conditions.
A previously unreported wake mixing phenomenon emerges at high frequencies
Results followed expectations up to a point. At low surge frequencies — around Stp ≈ 0.3 — wake recovery improved, consistent with prior work. As frequency increased, that benefit faded, and by Stp ≈ 3, the surging turbine’s wake looked nearly identical to a stationary one.
Then something unexpected happened. At surge frequencies approaching the blade passing frequency, wake recovery climbed again — sharply. The peak occurred when the difference between surge frequency and blade passing frequency equaled approximately 0.3, associated with natural energy modes in a fixed turbine’s wake. Power spectra confirmed a coherent structure forming at that difference frequency, resembling a helical wake pattern.
The researchers’ working hypothesis: the interaction between surge motion and rotor rotation excites a natural wake oscillation, generating a flow pattern similar to the deliberate “helix” wake mixing strategy already used in fixed offshore wind farms.
Thrust coefficient: the unexpected gatekeeper of wake recovery
Not all turbines responded equally to surge motion. The thrust coefficient — a measure of how much momentum the rotor extracts from the wind — proved decisive.
At CT = 0.58, surge motion produced negligible improvement: less than 3% gain compared to a stationary turbine. At CT = 0.80, improvement exceeded 15%. Higher thrust creates a steeper velocity gradient between the wake and surrounding free stream, producing unstable shear layers far more responsive to motion-induced disturbances.
The practical implication is pointed: operating conditions fundamentally shape whether surging helps the downstream wind farm. The same turbine, surging at the same frequency, can produce very different wake outcomes depending on how it’s being run.
What these findings mean for the future of floating wind
The newly identified high-frequency recovery regime isn’t a laboratory curiosity. For large-scale floating turbines in the 15 MW and above class, realistic wave-induced surge motions can produce Stp values well within the range where this phenomenon occurs — making it physically relevant to machines being deployed today.
Results held under turbulent inflow up to 4.7% turbulence intensity, suggesting real-world applicability. The researchers do caution, though, that model-scale turbulence characteristics don’t map perfectly to full-scale conditions.
What comes next is substantial. The wake mode needs characterization under complex inflows — wind shear, large-scale atmospheric structures, open-ocean conditions — before full-scale validation can begin. That validation remains the critical step before any of this informs actual wind farm design. Still, the discovery opens a concrete path: if surge motions near the blade passing frequency naturally generate beneficial wake mixing, future floating wind arrays may be designed — or actively controlled — to exploit that effect rather than simply tolerate it.
Learn more information: Schulz, C. W., Hölling, M., Peinke, J., and Messmer, T.: Brief communication: A novel wake mixing phenomenon and key parameters for wake recovery of floating wind turbines subjected to surge motions, Wind Energ. Sci., 11, 3775–3783, https://doi.org/10.5194/wes-11-3775-2026, 2026.
Daniel García is an Editor-in-Chief with strong expertise in structural work and engineering principles. He combines this technical foundation with deep knowledge of energy, spatial design, and emerging technologies, bringing a forward-thinking and analytical approach to editorial leadership.
