Flottement de drapeau : dynamique et couplage

Abstract : When flags flutter, they harvest the wind kinetic energy for producing periodic oscillations. Using flags for generating energy is then possible with flutter. Starting from this simple principle, this thesis deals with flag dynamics in the wind. In a wind tunnel, we study the forces on the flagpole of fluttering flags, focusing on the fluctuations of the flapping moment and drag. In particular, we observe strong variations of forces between different regimes of flutter characterized by a constant number of nodes. A model for flags is solved numerically with a Galerkin method and shows that during transitions between flutter regimes, the moment applied to the flagpole decreases because of the decrease of the flag curvature at the flagpole. When the flagpole is an oscillator with configurable inertia and stiffness, we report a strong coupling between the motion of the flag and its flagpole, with a frequency lock-in phenomenon. We study this coupling experimentally, and we show that a “stiffness-damping” parameter regulates the flagpole rotation. Notably, we design a coupling generating peak-to-peak rotations of 80o at wind speed of the order of 10 m/s.
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Contributor : Emmanuel Virot <>
Submitted on : Tuesday, June 16, 2015 - 7:29:46 PM
Last modification on : Wednesday, March 27, 2019 - 4:39:25 PM
Long-term archiving on : Tuesday, September 15, 2015 - 3:20:59 PM

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  • HAL Id : tel-01162549, version 2

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Emmanuel Virot. Flottement de drapeau : dynamique et couplage. Mécanique [physics.med-ph]. Ecole Polytechnique, 2015. Français. ⟨tel-01162549v2⟩

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