Coordinateurs du projet
Context
The FLOATEOLE attractiveness project will benefit from the complementary nature of the expertise of the host laboratory LHEEA in ocean engineering, atmospheric dynamics, and metrology, and the expertise developed by Sandrine Aubrun, who was appointed to the university professorship at Centrale Nantes in September 2017, Sandrine Aubrun, in the experimental characterization (wind tunnel and in-situ measurements) of wind turbine wakes and their interactions. By calling on several teams and test platforms within the laboratory, it will be used as a lever for the rapid integration of the candidate and will boost the implementation of her mission to coordinate the “offshore wind” activity across the laboratory.
Scientific breakthroughs and innovation
- Multidisciplinary approach to characterizing the wave/wind/structure coupling of a floating wind turbine.
- Emulation of the movements of a wind turbine float subjected to waves in an atmospheric boundary layer wind tunnel.
- Experiments conducted in controlled environments (atmospheric wind tunnel) and real environments (SEM-REV).
- Establishment of dynamic wake models dedicated to floating wind turbines.
Expected technical and economic impact
The FLOATEOLE project is part of the Hydrodynamics, Energy, and Atmospheric Environment Laboratory’s (LHEEA) commitment to contributing, through a multidisciplinary approach, to optimizing the operation of floating wind turbines by better understanding the consequences of coupling between the wind turbine and the water. Energy and Atmospheric Environment (LHEEA) to contribute, through a multidisciplinary approach, to optimizing the operation of floating wind turbines by better understanding the consequences of wave/wind/structure coupling on the performance and durability of wind turbines subjected to particularly hostile and non-deterministic operating conditions.
The aim is to combine wind tunnel and sea trials in order to characterize the effect of waves on the aerodynamic behavior of floating wind turbines and on the development of their wakes. Indeed, wake interactions, which are particularly intense in marine environments, have the dual disadvantage of reducing the available wind resource and increasing the structural fatigue of wind turbines. The effects of waves are emulated in the wind tunnel by the controlled movement of wind turbine models in order to reproduce idealized and then more realistic sea conditions. The unsteady behavior of the wake of wind turbines subjected to these movements is then characterized in order to propose wake meandering models adapted to floating wind turbines. This work is complemented by in-situ measurements using scanning lidar in the vicinity of the FLOATGEN project’s floating prototype wind turbine in order to capture relevant information on wind resources and wake under real wave conditions.
The FLOATEOLE project helps to consolidate the Pays de Loire region’s position in the field of offshore wind energy research by addressing a highly topical challenge: optimizing marine energy with a view to meeting the energy, climate, and socioeconomic challenges posed by the energy transition process.
Demonstrator
Emulator of the movements of a wind turbine float subjected to swell in an atmospheric boundary layer wind tunnel.
Results
The first year was mainly devoted to preparing the tools needed to launch the wind tunnel experimental phase of the FLOATEOLE project (conditioning and validation of the atmospheric wind tunnel, selection of the motion emulator). To this end, an engineering student on an end-of-study internship spent five months determining the specifications for the electromechanical system to be used in the wind tunnel to emulate the movements of the float. He also designed the experimental device used in the laboratory’s atmospheric wind tunnel to reproduce a marine-type atmospheric boundary layer on a very small scale. He carried out preliminary measurements, enabling the PhD student recruited in October 2018 to get off to an optimal start on his thesis work.
The second year was devoted to finalizing the reproduction of the marine atmospheric boundary layer at a scale of 1/500 and characterizing the flow downstream of a wind turbine model based on the porous disk concept. A device was also developed to reproduce the movements of a float at a scale of one degree of freedom. The first movement tested was a harmonic pitching motion. A parametric study of the amplitude and period of the movement was carried out and has already revealed a reduction in the turbulence rate at a distance of four diameter units downstream of the wind turbine model when subjected to pitching motion. These very recent results need to be supplemented and interpreted.
Vertical profiles of average velocity downstream of a floating wind turbine model as a function of the imposed pitching frequency.
The third year was devoted to a more detailed characterization of the impact of periodic yawing and swaying on wind wake dissipation. Velocity field measurements obtained using stereoscopic particle image velocimetry (Stereo-PIV) enabled the evolution of the wake to be observed over several diameters downstream of the wind turbine model. Additional data processing is required to characterize the physical mechanisms responsible for modifying the wake of floating wind turbines.
The definition of the specifications and the selection of the 3-degree-of-freedom displacement system were also finalized during this third year. Two systems were purchased in 2020 thanks to funding from this project, supplemented by the WEAMEC 3D4FLOATEOLE project.
Example of average velocity fields measured using stereo-PIV downstream of a floating wind turbine model.
The fourth year was devoted to characterizing the effects of three degrees of freedom (cavalier, pounding, and pitching) movements, either separate or simultaneous, idealized (harmonic) or realistic (broadband). A comb of nine hot wires distributed in a plane normal to the flow, at 4.6D and 8D downstream of the disk, was used to characterize the frequency response to these excitation motions of the distant wake. While a harmonic signature is clearly visible in the velocity spectra for idealized high-amplitude motions, a broader band modification of the spectral content of velocity fluctuations appears during more realistic motions.
Perspectives
The European H2020-MSCA-ITN FLOAWER (FLOAting Wind Energy netwoRk) project was launched on November 1, 2019. It comprises 10 beneficiary partners and 11 associated partners (academic and industrial). Centrale Nantes is the project coordinator. FLOAWER will train 13 early-stage researchers through a multidisciplinary program with the aim of designing more efficient and competitive floating wind turbines.
The FLOATEOLE project has also enabled collaboration with the German consortium involved in VAMOS (University of Stuttgart, TU Hamburg, DNV-GL and UL, DEWI, and Sowento). This project began in July 2019 for a period of three years. It will enable joint experimentation on FLOATGEN, collaboration on the use of measurements, and the study of wake models.