Synopsis: Dandelion Fluff Perfected for Flight

Calculations show that the number of white filaments springing from the top of a dandelion seed is optimized for steady flight, allowing the seeds to cruise long distances through the air.

A fluff-topped dandelion seed can float through the air for more than a kilometer before it drifts to the ground. In experiments last year, researchers revealed that the white filaments in the fluff—known collectively as a pappus—create a ring-shaped wake behind the seed that is associated with low pressure and acts to keep it aloft. Now Pier Giuseppe Ledda from the Swiss Federal Institute of Technology in Lausanne (EPFL) and colleagues have theoretically modeled the airflow around the pappus, reproducing the experimentally measured wake and showing that it provides the seed with steady flight capabilities. Ledda says that the results show that a simplified physics model can explain complex systems in the natural word. He also notes a practical side to the result—it could be used to aid in the design of light-weight parachute-like devices for objects that have a similar size and mass to dandelion seeds.

The team’s model approximates the pappus as a collection of rods that are arranged like the spokes of a bicycle wheel. Using standard equations from fluid dynamics, the team calculated the flow pattern that is created by the structure as it moves through the air. As in the experiments, they found that a ring-shaped vortex of circulating air forms directly behind the pappus, which they showed provides a wake that’s stable enough to carry the seed a long distance. Changing the number of spokes in the pappus, they found that steady cruising occurs when the pappus contains about 100 filaments—the same number found in real seeds. Ledda says that the result indicates that the morphology of the pappus has evolved to ensure stable flight.

This research is published in Physical Review Fluids.

–Katherine Wright

Katherine Wright is a Senior Editor for Physics.


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Fluid DynamicsInterdisciplinary PhysicsBiological Physics

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