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| Titel |
Laboratory modelling of resonant wave-current interaction in the vicinity wind farm masts |
| VerfasserIn |
Hans Gunnoo, Nizar Abcha, Maria-Isabel Garcia-Hermosa, Alexander Ezersky |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250103223
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| Publikation (Nr.) |
 EGU/EGU2015-2627.pdf |
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| Zusammenfassung |
| In the nearest future, by 2020, about 4% of electricity in Europe will be supplied by sea
stations operating from renewable sources: ocean thermal energy, wave and tidal energy, wind
farms. By now the wind stations located in the coastal zone, provide the most part of
electricity in different European countries. Meanwhile, effects of wind farms on the
environment are not sufficiently studied.
We report results of laboratory simulations aimed at investigation of hydrodynamic fields
arising in the vicinity of wind farm masts under the action of currents and surface waves. The
main attention is paid to modeling the resonance effects when the amplitude of velocity
pulsations in the vicinity of the masts under the joint action of currents and harmonic
waves demonstrate significant growth. This resonance can lead to an increase in
Reynolds stress on the bottom, intensification of sediment transport and sound
generation.
The experiments are performed in the 17 meters hydrodynamical channel of laboratory
Morphodynamique Continentale et Côtière UMR CNRS 6143. Mast are modeled by vertical
cylinder placed in a steady flow. Behind the cylinder turbulent Karman vortex street occurs.
Results are obtained in interval of Reynolds numbers Re=103 – 104(Re=Ud/v, where U is the
velocity of the flow, d is diameter of the cylinder, ν is cinematic viscosity). Harmonic surface
waves of small amplitude propagating upstream are excited by computer controlled wave
maker. In the absence of surface waves, turbulent Karman street with averaged frequency f is
observed. It is revealed experimentally that harmonic surface waves with a frequencies
closed to 2f can synchronize vortex shedding and increase the amplitude of velocity
fluctuations in the wake of the cylinder. Map of regimes is found on the parameter
plane amplitude of the surface wave - wave frequency. In order to distinguish the
synchronization regimes, we defined phase of oscillations using the Hilbert transform
technique.
We investigate effect of hydrodynamic turbulence on synchronization of hydrodynamic
wake by surface waves. To change the level of turbulence we used honeycombs. Measuring
the velocity upstream the cylinder, we found that under our experimental conditions
honeycombs can reduce the level of hydrodynamic turbulence in two times. It is found that
intensity of turbulence determines the amplitude threshold of synchronization in the wake
behind cylinder.
The physical mechanisms of synchronization, its impact to the Reynolds stress and the
possibility of such a resonance in the vicinity of masts located in the coastal zone are
discussed.
This work was supported by the OFELIA (Offshore Foundations Environmental
Impact Assessments) project in the frame of the European cross-border cooperation
programme INTERREG IV A France (Channel) - England, co-funded by the ERDF. |
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