Vertical wake deflection for floating wind turbines by differential ballast control

Nanos, Emmanouil M.; Bottasso, Carlo L.; Manolas, Dimitris I.; Riziotis, Vasilis A.

doi:10.5194/wes-2021-79

Cited by 4 publications

(5 citation statements)

References 25 publications

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“…From Figure 7, for the below-rated wind speed scenario, this center is half a diameter higher than the hub height, which implies that the wake deflects upwards. This phenomenon has been previously observed by Wise and Bachynski, 19 Doubrawa et al, 51 and Nanos et al, 52 for below-rated wind speeds. The reason behind this deflection is the non-zero vertical component of the thrust that the incoming flow experiences when encountering a rotor with a specific tilt with respect to the ground.…”

Section: Results On Deficit and Meanderingsupporting

confidence: 80%

Effect of atmospheric stability on the dynamic wake meandering model applied to two 12 MW floating wind turbines

Rivera‐Arreba,

Wise,

Eliassen

et al. 2023

Wind Energy

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Current global analysis tools for floating wind turbines (FWTs) do not account for the combined effects of atmospheric stability and wakes from neighboring turbines. This work uses the mid‐fidelity dynamic wake meandering model, together with turbulent wind fields generated based on stable, neutral, and unstable atmospheric conditions, to study the low‐frequency content of the global responses of two semisubmersible FWTs separated by eight rotor diameters. Incoming wind fields based on the Kaimal spectrum and exponential coherence model, the Mann spectral tensor model, and a time‐series input‐based turbulence model are used. The respective input parameters for these models are fitted to high‐fidelity large eddy simulation data.In unstable, below‐rated conditions, meandering leads to an increase in the yaw standard deviation of the downwind turbine of almost three times larger than the upwind turbine. Deficit and the upwards wake deflection affect the mean pitch and yaw, especially for the below‐rated wind speed scenario. The mean pitch of the downwind turbine is reduced up to half the mean pitch value of the upwind turbine, whereas the mean yaw changes direction due to the enhanced effect of shear. The effect of meandering on the structural loading is highest on the standard deviation of the tower‐top yaw moment of the downstream turbine, which increases more than 2.2 times compared to the upwind turbine value. Based on these findings, atmospheric stability affects wake deficit and meandering which in turn have a profound effect on the low‐frequency global motions and structural response of floating wind turbines.

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Section: Results On Deficit and Meanderingsupporting

confidence: 80%

Effect of atmospheric stability on the dynamic wake meandering model applied to two 12 MW floating wind turbines

Rivera‐Arreba,

Wise,

Eliassen

et al. 2023

Wind Energy

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“…Finally, regarding the impact of the motion of the floater on the wake characteristics, the amplitude of the surge and sway motions used in this study was relatively small compared to the values used in numerical (Nanos et al, 2021;Chen et al, 2022) and wind tunnel (Fu et al, 2019;Schliffke et al, 2020) studies that focused on the study of the effect of the wind turbine motion on the wake characteristics. Comparing the standard deviation of the surge motion speed with the longitudinal speed showed that the standard deviation of the wind was one order of magnitude larger.…”

Section: Discussionmentioning

confidence: 96%

“…In the case of floating wind turbines, the wind turbine motion that results from the interaction of the floating structure with the wind and sea has to be considered, in addition to the atmospheric conditions. The wake characteristics of floating wind turbines have been studied using numerical (Wise and Bachynski, 2020;Kleine et al, 2021;Nanos et al, 2021;Chen et al, 2022;Li et al, 2022) and wind tunnel (Fu et al, 2019;Schliffke et al, 2020) experiments. Those studies focussed on the impact of the sway (Fu et al, 2019;Nanos et al, 2021;Li et al, 2022), surge (Fu et al, 2019;Schliffke et al, 2020;Chen et al, 2022) and heave (Kleine et al, 2021) motions on the turbine operation.…”

Section: Introductionmentioning

confidence: 99%

“…The wake characteristics of floating wind turbines have been studied using numerical (Wise and Bachynski, 2020;Kleine et al, 2021;Nanos et al, 2021;Chen et al, 2022;Li et al, 2022) and wind tunnel (Fu et al, 2019;Schliffke et al, 2020) experiments. Those studies focussed on the impact of the sway (Fu et al, 2019;Nanos et al, 2021;Li et al, 2022), surge (Fu et al, 2019;Schliffke et al, 2020;Chen et al, 2022) and heave (Kleine et al, 2021) motions on the turbine operation. Yet, the absence of the study of the motion of floating turbine under realistic atmospheric turbulence conditions limits our understanding on how the impact of the motion of the wind turbine on the wake properties can be utilized in control strategies that optimize the operation of wind turbines and subsequently wind farms.…”

Section: Introductionmentioning

confidence: 99%

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Revealing inflow and wake conditions of a 6MW floating turbine

Angelou

Mann

Dubreuil-Boisclair

2023

Preprint

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Abstract. We investigate the characteristics of the inflow and the wake of a 6MW floating wind turbine from the Hywind Scotland offshore wind farm, the world's first floating wind farm. We use two commercial nacelle-mounted lidars to measure the up- and downwind conditions, with a fixed and a scanning measuring geometry, respectively. In the analysis, the effect of the surge and sway motion of the nacelle on the lidar measuring location is taken into account. The upwind conditions are parameterised in terms of the mean horizontal wind vector at hub height, the shear and veer of the wind profile along the upper part of the rotor and the induction of the wind turbine rotor. The wake characteristics are studied in two narrow wind speed intervals 8.5–9.5 ms-1 and 12.5–13.5 ms-1, corresponding to below and above rotor rated speeds, respectively, and for turbulence intensity values between 3.3 %–6.4 %. The wake flow is measured by a wind lidar scanning in a horizontal plan position indicator mode, which reaches ten rotor diameters downwind. This study focuses on the downstream area between 3 and 8 rotor diameters. In this region, our observations show that the transverse profile of the wake can be adequately described by a self-similar wind speed deficit, that follows a Gaussian distribution. We find that even small variations (∼1 %–2 %) of the ambient turbulence intensity can result in an up to 10 % faster wake recovery. Furthermore, we do not observe any additional spread of the wake due to the motion of the floating wind turbine.

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“…The vertical and horizontal deflection are a consequence of the built-in shaft tilt (referred to as shaft tilt in the following) and vertical shear, and yaw misalignment, respectively. For floating wind turbines (FWTs), and specifically for low wind speed conditions, several authors [1][2][3] have reported the deflection of the wake not only because of the FWT shaft tilt, but also due to the platform pitch angle. This phenomenon, combined with the variation in the projected area of the rotor, affects both the produced power and the loads of the FWT in the wake.…”

Section: Introductionmentioning

confidence: 99%

Effect of the vertical wake deflection on the response of a 12MW semisubmersible FWT

Rivera-Arreba,

Eliassen,

Bachynski-Polić

2023

J. Phys.: Conf. Ser.

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The need to understand the interaction of floating wind turbines operating in the marine boundary layer with other surrounding turbines is of increasing importance as wind farms and rotor sizes get larger. For low wind speed conditions, the wake deflects upwards due to the floating wind turbine built-in rotor tilt and the platform pitch angle. Furthermore, based on field data from the North Sea, a convective atmosphere is likely to occur, especially for lower wind speeds. It is therefore key to understand the combined effect of meandering, wake deflection and atmospheric stability for low wind speed conditions on the floating wind turbines in a wind farm. In this work, to account for atmospheric stability, data from large-eddy simulation (LES) for a 7.5m/s wind speed scenario and three atmospheric stability conditions, are used as input to FAST. Farm to study the effect of the wake deflection upwards on a 12 MW semisubmersible placed 8 rotor diameters (D) downwind of a stationary wind turbine. Three built-in shaft tilt angles cases are considered for the fixed upwind turbine: 12°, 6° and no tilt angle. The main effects of the wake deflection are on the power output of the floating wind turbine in the wake, and on the tower top yaw moment. For stable conditions, the mean tower top yaw moment increases by more than three times. The findings of this work contribute to the investigation of the wake deflection as a control strategy to minimize wake losses in floating wind farms.

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Vertical wake deflection for floating wind turbines by differential ballast control

Cited by 4 publications

References 25 publications

Effect of atmospheric stability on the dynamic wake meandering model applied to two 12 MW floating wind turbines

Effect of atmospheric stability on the dynamic wake meandering model applied to two 12 MW floating wind turbines

Revealing inflow and wake conditions of a 6MW floating turbine

Effect of the vertical wake deflection on the response of a 12MW semisubmersible FWT

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