Dandelion-Inspired Aerodynamics

The dandelion diaspore has one of the most efficient dispersal mechanisms in the plant realm. Its filamentous structure allows a high area per unit volume. The filament diameter maximises drag per unit area. The filament's interaction is revealed by a Separated Vortex Ring (SVR) in its wake. To investigate its aerodynamics, we consider a simplified model made of a disk with uniform permeability. The Reynolds and the Darcy numbers govern the drag and result in a wide range of wake topologies, from a steady axisymmetric SVR to chaotic. We study the dandelion's dynamic response to wind perturbations. We developed a unique bespoke wind tunnel to replicate uniform, irrotational, horizontal gusts. We discovered that such gusts result in an upward force on any free-falling body, including impervious infinite-span cylinders with rectangular and circular sections. The resulting altitude gain depends on gust accelerations, density ratio, nondimensional inertia, and Galilei number. We conjecture that the dandelion has a stem length optimising inertia for gust response with minimal increase in Galilei number. Ongoing work includes the investigation of the dandelion in turbulence and the development of dandelion-inspired drones, dandidrones, for swarm sensing.