High-resolution bathymetry of the Alderney Race and its geological and sedimentological description (Raz Blanchard, northwest France)

Furgerot, Lucille; Poprawski, Yohann; Violet, Marc; Poizot, Emmanuel; Bois, Pascal Bailly du; Morillon, Mehdi; Méar, Yann

doi:10.1080/17445647.2019.1657510

Cited by 21 publications

(18 citation statements)

References 24 publications

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“…Ikhennicheu et al [15] studied the wake of various elementary obstacles used to experimentally reproduce bathymetry variations, like those encountered in the Alderney Race in the middle of the English Channel. Such bathymetry variations have been observed in-situ, according to the geological description of this particular place presented by Furgerot et al [7]. They concluded that a unique and wide obstacle, i.e.…”

Section: Introductionmentioning

confidence: 57%

Experimental analysis of the shear flow effect on tidal turbine blade root force from three-dimensional mean flow reconstruction

Gaurier

Druault

Ikhennicheu

et al. 2020

Phil. Trans. R. Soc. A.

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In the main tidal energy sites like Alderney Race, turbulence intensity is high and velocity fluctuations may have a significant impact on marine turbines. To understand such phenomena better, a three-bladed turbine model is positioned in the wake of a generic wall-mounted obstacle, representative of in situ bathymetric variation. From two-dimensional Particle Image Velocimetry planes, the time-averaged velocity in the wake of the obstacle is reconstructed in the three-dimensional space. The reconstruction method is based on Proper Orthogonal Decomposition and enables access to a representation of the mean flow field and the associated shear. Then, the effect of the velocity gradient is observed on the turbine blade root force, for four turbine locations in the wake of the obstacle. The blade root force average decreases whereas its standard deviation increases when the distance to the obstacle increases. The angular distribution of this phase-averaged force is shown to be non-homogeneous, with variation of about 20% of its time-average during a turbine rotation cycle. Such force variations due to velocity shear will have significant consequences in terms of blade fatigue. This article is part of the theme issue ‘New insights on tidal dynamics and tidal energy harvesting in the Alderney Race’.

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Section: Introductionmentioning

confidence: 57%

Experimental analysis of the shear flow effect on tidal turbine blade root force from three-dimensional mean flow reconstruction

Gaurier

Druault

Ikhennicheu

et al. 2020

Phil. Trans. R. Soc. A.

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“…Ikhennicheu et al [23] present a case study comparison of various elementary obstacles used to reproduce bathymetry variations, like those encountered in the Alderney Race (middle of the English Channel), as shown by its geological description by Furgerot et al [24]. They concluded that wide obstacles (6 times wider than its height) produces the most energetic wake that extends up to the free surface.…”

Section: Introductionmentioning

confidence: 99%

Experimental study of bathymetry generated turbulence on tidal turbine behaviour

et al. 2020

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In high flow velocity areas like those suitable for tidal applications, turbulence intensity is high and flow variations may have a major impact on tidal turbine behaviour. A three-bladed horizontal axis turbine model (scale 1:20) is positioned in the wake of a square wall-mounted cylinder, representative of specific in situ bathymetric variation, to experimentally study these effects in a current flume tank. Local and global loads are acquired in synchronisation with velocity measurements to study the turbine response to flow fluctuations. Velocity measurements need to be obtained close to the turbine, contrary to what is commonly considered, to properly correlate velocity and loads fluctuations. Results show that the loads phase average and their dispersion evolve according to the sheared velocity profile. We conclude that the turbine load fluctuations directly respond to the low frequency velocity fluctuations and are dominated by the turbulent structures shed from the cylinder. It is then possible to compare the effects of large coherent turbulent structures on the turbine behaviour to cases with more classical free stream turbulence commonly studied. These results provide a substantive database in high Reynolds number flows for further fatigue analysis or recommendations for turbine positioning in such flows.

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“…However, two conditions obliged us to change the location. A preliminary study revealed that, in the northern sector, the seafloor is mostly composed of Proterozoic crystalline rocks that exhibit a dense fracture network and form a highly irregular topography [15]. Therefore, our ADCP support platforms were thought to be more unstable there.…”

Section: Data and Methodsof Analysis (A) Static Point Velocity Measurmentioning

confidence: 99%

“…According to a numerical study by Coles et al [13], the maximum power that can be extracted in this shallow water 15km-wide strait, is estimated at 5.1 GW, which is 35% more than a previous estimate proposed by Draper et al [14] for the Pentland Firth (UK). The complexity of local hydrodynamics and the interaction between the highly irregular bottom topography [15], powerful tidal stream and high waves was highlighted in a number of numerical studies devoted to this geographic area (e.g. [16][17][18]).…”

Section: Introductionmentioning

confidence: 99%

One year of measurements in Alderney Race: preliminary results from database analysis

Furgerot¹,

Sentchev

Bois³

et al. 2020

Phil. Trans. R. Soc. A.

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The Alderney Race is assumed to have the largest tidal-stream energy potential in the north-western European coastal seas. Interaction of the powerful tidal stream with strong wind, high waves and irregular bathymetry creates hydrodynamic conditions of extreme complexity, with high levels of turbulence. A comprehensive dataset has been created to improve the understanding of physical processes, turbulence, tidal stream and resource variability at the site. The database contains a large amount of oceanographic and meteorological measurements acquired in Alderney Race in 2017–2018. This exceptionally long period of observations (nearly one year) became possible due to modern tools and strategies of data acquisition. The paper presents some significant results from the database analysis. Among many results, we would like to underline the following: (i) a wide range of variability of mean flow and sea state parameters was documented; (ii) exceptionally large values of current velocity (7 m s −1 ) and significant wave height (8 m) were measured during extreme meteorological conditions; (iii) high-frequency variability of current speed during storm events was also found to be very large, with the standard deviation of velocity reaching 0.3 m s −1 in the bottom boundary layer, and 0.6 m s −1 in the surface layer; and (iv) predominant wind and wave direction relative to the flow impacts the wave height and significantly increases the turbulence kinetic energy of the flow. To our knowledge, this is the largest multi-variable database available on potential tidal energy sites. The results of database analysis can represent a significant advance in environmental conditions and resource characterization and provide advanced information to turbine developers. This article is part of the theme issue ‘New insights on tidal dynamics and tidal energy harvesting in the Alderney Race’.

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High-resolution bathymetry of the Alderney Race and its geological and sedimentological description (Raz Blanchard, northwest France)

Cited by 21 publications

References 24 publications

Experimental analysis of the shear flow effect on tidal turbine blade root force from three-dimensional mean flow reconstruction

Experimental analysis of the shear flow effect on tidal turbine blade root force from three-dimensional mean flow reconstruction

Experimental study of bathymetry generated turbulence on tidal turbine behaviour

One year of measurements in Alderney Race: preliminary results from database analysis

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