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Comparison of samaras movement between free falls and constrained rotation, using high speed imaging and stereocorrelation

Abstract : The maple seed, or samara, presents a relatively stable rotational movement after a transitional phase, that allows it to create a high lift and therefore promotes dissemination. This important lift force comes from little vortex created close to the wing, thanks to its shape. This phenomenon is also present for birds and insects. It leads to a spin velocity of samaras between 80 and 150 rad.s-1 and a descending velocity of around 1 m.s-1. The center of rotation approximately coincides with the center of gravity for maple seeds, and it has been observed that this center describes a helical descending movement; it is also the case for mechanical resin samaras. In the study presented here, the behavior of samaras (Acer palmatum) during their free fall was analyzed, in order to valid their characteristic parameters (spin velocity and descending velocity). Then, samaras were placed in a wind tunnel with their axis of rotation xed, and their translation movement stopped. They could always auto-adapt their angular position to the air flow. The relative air speed in the tunnel has been set at the value measured during free falls, to compare the two behaviors. Stereocorrelation has been used with high speed cameras because of the speed of movement (several revolutions per second). The velocities of each point of the samaras were measured by stereo image correlation. Then, from this velocity field, the instantaneous center of rotation, rotation vector and velocity vector of the seeds were identi ed by optimization considering a rigid body motion. During the free fall experiments, due to the limited depth of fi eld of the objectives, only a quarter of a revolution could be exploited. Whereas in the constrained tests, the samaras are horizontally stable, so their whole movement is in the depth of field. Finally, the differences of movement characteristics between the two setups have been analyzed, to see if a biomimicry application could be valuable for energy harvesting.
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Conference papers
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https://hal.archives-ouvertes.fr/hal-01813218
Contributor : Aurélien Carré <>
Submitted on : Tuesday, June 12, 2018 - 10:32:35 AM
Last modification on : Saturday, February 29, 2020 - 6:40:25 PM

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  • HAL Id : hal-01813218, version 1

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Aurélien Carré, Émile Roux, Laurent Tabourot, Pierre Vacher, Ludovic Charleux. Comparison of samaras movement between free falls and constrained rotation, using high speed imaging and stereocorrelation. 12th European Fluid Mechanics Conference, Sep 2018, Vienna, Austria. ⟨hal-01813218⟩

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