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Flexibility reduces drag: daffodil

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Daffodil / Agunther / LicenseCC-by - Attribution

The flowers of daffodils twist in the wind, reducing drag because of their torsional flexibility due to stem noncircularity.

BIOMIMICRY TAXONOMY
Summary
"And daffodil flowers, borne off to one side of their stems, swing around similarly, reducing their drag by about 30 percent in the process (Etnier and Vogel 2000). Twisting in the wind isn't just a slogan left over from the Nixon presidency. Daffodils appear to 'dance' in the wind, as noted by the poet William Wordsworth, because down near ground level, winds are especially puffy." (Vogel 2003:382)

"Daffodil flowers extend laterally from the long axes of their stems; as a result, wind on a flower exerts torsional as well as flexural stress on the stem. Stems respond by twisting, and thus flowers reorient to face downwind in moderate winds, in the process reducing their drag by ∼30%. This repositioning is facilitated by the stems' relatively low torsional stiffness. Daffodil stems have a ratio of flexural to torsional stiffness of 13.27 ± 0.96 (SD), compared with 8.33 ± 3.20 (SD) for tulip stems, which bear flowers as symmetrical extensions of their long axes, and compared with 1.5 for isotropic, incompressible, circular cylinders." (Etnier and Vogel 2000:29)
About the inspiring organism
Med_daffodil Narcissus
Narcissus
Common name: Daffodil

Learn more at EOL.org
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist


Bioinspired products and application ideas

Application Ideas: Incorporating materials with torsional flexibility into building designs and structures, particularly in coastal cities prone to wind storms and hurricanes; microstructures on wind turbine blades that allow them to continue functioning in high winds; wind turbine towers that flex with the wind; more aerodynamic cars, semi trailers and cabs, with structures that 'twist' to reduce drag.

Industrial Sector(s) interested in this strategy: Architecture, construction, structural engineering, wind energy, automotive, transportation

Experts
Steven Vogel

Biology Department, Duke University
References
Steven Vogel. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
Learn More at Google Scholar Google Scholar  

Etnier SA; Vogel S. 2000. Reorientation of Daffodil (Narcissus: Amaryllidaceae) Flowers in Wind: Drag Reduction and Torsional Flexibility. American Journal of Botany. 87(1): 29-32.
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Comments

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Sherry
over 4 years ago
Thanks to Duarte Miguel Prazeres for finding and uploading these photos.
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ernstjanm
over 5 years ago
currently an electric scooter is being developed at the Delft Technical University in the Netherland, incorporating this strategy by featuring a flexible body textile body, passively reacting to hardy Dutch "polder-" winds.
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