Nature 562, 414–418 (2018)
Weed though it may be, the common dandelion is savvy when it comes to dispersing its seeds (pictured). Once separated from the head, the seeds remain airborne with the help of a bundle of drag-enhancing bristles known as a pappus. This structure itself isn’t an obvious bet for enabling the formidable distances the seeds cover: other species adopt wing-like structures in dispersal. But now, Cathal Cummins and colleagues have found that the bristly pappus induces a vortex of recirculating fluid that offers the requisite lift.
By visualizing the flow around the seeds, Cummins et al. found that for low Reynolds number, neighbouring bristles interact strongly due to the boundary layer around each filament. This in turn reduces airflow through the pappus, conferring a high drag coefficient. The team showed that a structure with a similar porosity could reproduce this flow behaviour, suggesting that pappus porosity is tuned to simultaneously stabilize the vortex and optimize aerodynamic loading.
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Klopper, A. Flight of the dandelion. Nature Phys 14, 1071 (2018). https://doi.org/10.1038/s41567-018-0350-2
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DOI: https://doi.org/10.1038/s41567-018-0350-2