Dandelion seeds can fly up to 100 km, and now we know how
The dandelion seed is about 90 per cent porous, which forms a powerful vortex above the seed
The dandelion seed holds the record as the farthest travelling passive flying structure that we know of in the plant world, flying up to 100 kilometres. Now, researchers from the University of Edinburgh have discovered the secret to the flight of the dandelion, and it could improve future drone technology.
A dandelion only has between 100 and 110 filaments, or thread-like fibres, on the head of the seed. But it has four times more flight time than predicted by any fluid mechanics calculations.
It comes down to a newly described type of vortex, or whirlwind, that forms in the air around the dandelion seed's filaments.
The discovery by researchers from the University of Edinburgh was published yesterday in Nature.
"What we discovered is that the key mechanism to enable this vortex is to have air flow through a porous material, and the amount of porosity is of paramount importance to enable the stability of the vortex," said Ignazio Maria Viola, a senior author on the study.
For the dandelion, the seed head is about 90 per cent porous. The vortex is produced by the disruptions to the air as the air passes across each individual filament. The number of 100–110 filaments is crucial to making sure the air forms that vortex and can suck up the seed and keep it aloft.
Additionally, the researchers say the placement and number of dandelion filaments allow it to disperse to new environments.
"What we found was that the flow around each filament interacts strongly with the flow around neighbouring filaments," said Cathal Cummins, lead author on the paper. "And this flow is such that flow between filaments is significantly slowed down. And so you get this, what we call, a wall effect."
So the dandelion seed is 90 per cent space, yet it acts better than a solid parachute by taking advantage of this type of vortex.
The discovery required building custom equipment to create the effect of a dandelion seed wind tunnel and track its flight path. They also took long exposure photographs and video to help with their measurements and analysis.
"We put dandelions inside the wind tunnel, then injected smoke into the wind tunnel so that the smoke followed which way the air was moving around the dandelion," said Cummins. "Then we illuminated just a thin sliver of that flow field with a powerful laser."
The research suggests this design works well at a very small scale and hope it can be useful to improve drone technology to use less energy and extend flight duration.