Flexibility reduces drag: daffodil

1 of 2 Daffodil / Martin Hirtr.. / License

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

Biomimicry Taxonomy

	Maintain physical integrity >
	Protect from abiotic factors >
	Wind

Biomimetic Application Ideas

Incorporating materials with torsional flexibility into building designs and structures Microstructures on wind turbine blades that allow them to continue functioning in high winds More aerodynamic cars, semi trailers and cabs, with structures that 'twist' to reduce drag

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[Collapse all sections] 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

Narcissus
Narcissus
[Daffodil]

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.

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

Thanks to Duarte Miguel Prazeres for finding and uploading these photos.

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