Abstract

In this talk I will provide a brief overview of the research on applied fluid dynamics and vortex-dominated flow in my research group, and I will present in-depth our recent findings on the flight of the dandelion fruit (https://doi.org/10.1038/s41586-018-0604-2).

The dandelion uses a bundle of bristles, known as the pappus, to enhance the drag and to slow down its descent. This passive flight mechanism allows the dandelion to be carried by the wind for even hundreds of miles. The underlying fluid dynamics of this drag-enhancing mechanism was, however, unknown. We found that when the dandelion falls, the air flows through the pappus and forms a bubble of recirculating flow. This bubble, which we named the separated vortex ring (SVR), sits stably a few millimetres above the dandelion, like a halo.

In this talk I will describe how we discovered this extraordinary new type of vortex, and what we have learnt of it. The discovery of the SVR suggests the existence in nature of a new type of locomotion. We envisage that this discovery might contribute to explain the function of many hairy structures in the plant and animal kingdoms. We also envisage that it may contribute to the design of micro aerial vehicles that will be passively carried by the wind.

The research on the dandelion fruit is a collaboration with the research groups of Dr Naomi Nakayama (School of Biological Sciences) and Dr Enrico Mastropaolo (School of Engineering) at the University of Edinburgh.