Loading effects on floating offshore horizontal axis wind turbines in surge motion

Abstract

a b s t r a c tPrevious experimental work under controlled conditions on a small scale floating offshore horizontal axis wind turbine has shown an increasing amplitude of the cyclic thrust and power generation against tip speed ratio under the influence of surge motion. A numerical study is performed using an actuator disc Navier Stokes model, a Blade Element Momentum model and a Generalized Dynamic Wake model on the NREL 5 MW reference rotor in order to confirm or reject these observations on a full-scale surging rotor. The hypothesis was confirmed and the underlying reasons for the observed behaviour were studied on the basis of the near wake physics. It was found that the analysis of transient effects such as fatigue cannot be performed without an adequate aerodynamic model of the wake. Characterization of quasisteady and unsteady regimes may be useful to establish when detailed aerodynamic wake models are necessary.

Numerical analysis of unsteady aerodynamics of floating offshore wind turbines

“…Bayati et al [8] evaluated the unsteady aerodynamics of floating offshore wind turbines as function of the amplitude and frequency of mono-harmonic surge and pitch motions. Micallef and Sant [10] confirmed numerically the experimental statement of Sant et al [3], that the amplitude of thrust cyclic response to surge motion increases with increasing tip speed ratio. He underlined the importance of an adequate aerodynamic model of the wake for an accurate estimation of the structure fatigue.…”

“…Moreover, as highlighted by Micallef and Sant [10], an adequate determination of the wake dynamics is crucial for an accurate evaluation of the structural loads. As most of the energy of the wake is transported by the tip vortices, the current analysis focuses on their dynamics.…”

“…A few analyses also evaluated the ability of engineering models to predict the loads. For example, while de Vaal et al [2] showed that current dynamic wake models in blade element momentum models (BEM) are suitable for global load analysis, Micallef and Sant [10] showed that BEM suitability highly depends on the wave conditions. Most of the numerical analyses are based on simplified approaches, like wake dynamic models, BEM theory or Generalized Dynamic Wake model (GDW), and take as reference simulations with the actuator disc model.…”

On the power coefficient overshoot of an offshore floating wind turbine in surge oscillations

“…Variation of C P against λ , without platform oscillation. Comparison case: “BEM‐FAST”, “GDW‐FAST”, and “AD” from Micallef and Sant; “GH Bladed”, “FVM‐WInDS”, and “Experiment” from Farrugia et al [Colour figure can be viewed at wileyonlinelibrary.com]…”

Wake to wake interaction of floating wind turbine models in free pitch motion: An eddy viscosity and mixing length approach

“…They found a slight increase in power production of the moving turbine when compared to a stationary and also a decrease in Reynolds shear stress, with the conclusion of a weaker recovering of the wake in the floating case. Experimental and numerical [16,17] investigations of floating turbines in surge motion have shown an increase of thrust and power variations with increasing tip speed ratios of the turbines, with good agreement of experimental and numerical results for rated tip speed ratios and below. Sebastian et al [18] performed numerical investigations on unsteady aerodynamics of floating wind turbines and found the pitch motion of a floating platform being one major contributor to unsteady flow effects.…”