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Couplage entre la dynamique du vent et le mouvement d'un couvert végétal

Abstract : Wind fluctuations over plant canopies are governed by a mixing layer (or Kelvin-Helmholtz) type instability,
linked to the inflection of the mean wind profile at the top of the canopy. Here the coupling between wind dynamics and the waving of crop canopies under wind is explored.

A new experimental technique is developped for on-site measurements of the spatio-temporal motion of a crop canopy. The wind-induced motion of wheat or alfalfa
canopies is video-recorded. An image correlation technique, based on PIV algorithms (Particle Image Velocimetry), then allows to derive the bi-dimensional spatio-temporal velocity field of the canopy surface. The coherent part of the motion is extracted by a
bi-orthogonal decomposition of the velocity field. It is shown that the corresponding space and time
features cannot be explained using predictions from the mixing layer analogy of wind above canopies, which is the most common model in this environment. We demonstrate that the plants dynamics, via their natural vibration frequency, plays an important role in the frequency and wavelength selection for the coherent motion of the canopy.

A fully-coupled model, where wind fluctuations and canopy motion interact through a drag term, is then proposed. A linear stability analysis allows to emonstrate a lock-in mechanism, whereby the frequency of the instability deviates from the Kelvin-Helmholtz law and locks on the natural frequency of the plants. This finding is then compared to the experimental results from on-site measurements, and good agreement, in both frequency and wavelength of the propagating patterns observed on the canopy surface, is shown.
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Contributor : Christiane Tribillon <>
Submitted on : Wednesday, February 1, 2006 - 10:16:34 AM
Last modification on : Wednesday, March 27, 2019 - 4:39:25 PM
Long-term archiving on: : Saturday, April 3, 2010 - 8:09:24 PM

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Charlotte Py. Couplage entre la dynamique du vent et le mouvement d'un couvert végétal. Dynamique des Fluides [physics.flu-dyn]. Ecole Polytechnique X, 2005. Français. ⟨tel-00011511⟩

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