丁香园AV

Synopsis

Dandelions (Taraxacum officinale) are perennial herbs that disperse their seeds using wind and convective updrafts. Each seed is suspended by a bunch of bristles called the pappus, which prolongs the descent of the seed enabling it to be carried further by winds. However the physics-archive underlying pappus-mediated flight has been unresolved. In this work, the analysis of the flight mechanism of the Dandelion uncovers an extraordinary type of vortex (a ring of recirculating fluid) which is neither attached nor advected downstream and is therefore called a separated vortex ring (SVR). The circular disc-like geometry and the porosity of the pappus are key features that enable the formation of a SVR, which was thought to be too unstable to occur. This discovery of SVRs demonstrates a novel type of fluid behavior around fluid-immersed bodies.

Reference: 1. Cummins C. et al, A separated vortex ring underlies the flight of the dandelion, Nature, vol 562 (2018).