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| Titel |
Vortex dynamics around an immersed structure |
| VerfasserIn |
Adrien Poupardin, Nicolas Bourneton, Grégory Pinon, Elie Rivoalen, Jérôme Brossard, Gaele Perret |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250046125
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| Zusammenfassung |
| Abstract:
The interaction of waves and current with submerged structures in coastal zones generates
some complex hydrodynamics features which may considerably impact the local
environment. The geometrical singularities of the structures produce concentrated vortex
filaments which may impact the sea bed and/or the free surface.
The objective of the present study is to characterize the vortex dynamics generated by a
horizontal thin plate considered as a vortex generator, in a regular wave field. Vortices are
generated at the edges of the plate. They are deformed and destroyed by three-dimensional
instabilities. Their dynamics is investigated thanks to laboratory experiments conducted in a
10 m long wave flume.
The two-dimensional vortex dynamics is characterized using PIV measurements. For this
experiment, mean velocity and vorticity fields all around the plate are determined in different
instants for one wave period. Then, we observe the formation of downstream and upstream
vortex pairs which are mutually advected toward the sea bed and the free surface respectively.
These evolutions are characterized through mean vortex trajectories calculated thanks to the
mean velocity fields. It shows the presence of a stagnation point at the downstream flume
bottom due to the vortex pair advection and to the presence of an adjacent recirculation cell
under the plate. This point will be a location of scouring phenomenon at the sea
bed.
To test different geometries and wave conditions a lagrangian simulation (using vortex
method) of the experiment has been developed to reproduce numerically the vortex
wake in non stationary, two-dimensional flows. The numerical results agree with
experiments.
The three-dimensional dynamics is studied thanks to stereo photography. The vortex
cores are visualised with hydrogen micro bubbles generated at the edges of the plate by
electrolysis. The evolution and the destabilization of the vortices are recorded by two CCD
cameras focus in two different planes. Thanks to this technique, the vortices are reconstructed
in the three dimensions of the space in different instants and for several wave periods. These
three-dimensional instabilities are characterized by several deformation modes whose
wavelength and growth rate are determined by signal processing and spatiotemporal vortex
oscillations analyzes. By varying the geometry and the wave conditions we determine
how these parameters control the observed three-dimensional vortex instabilities.
A control of the vortex breakdown could be considered through modification of
the edge of the plate geometry to avoid scouring phenomenon in the sea bed for
example.
Key words:
Vortex dynamics – Marine structures – Wake – Environmental impacts – Vortex
three-dimensional instabilities |
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