Flying on the canopy of dandelion seeds
Flying on the canopy of dandelion seeds lead image
Dandelion seeds gracefully fly in the wind, using their fluffy halos to spread the flowering plant’s reach. Unlike the wings of birds and insects, honed to reduce aerodynamic drag, dandelion seeds use drag to stay afloat and are wholly dependent on surrounding airflow.
This low-effort flying mechanism is an appealing model for a bio-inspired, unpowered aircraft. However, in turbulent conditions or increased Reynolds numbers, such an aircraft could become unstable, so identifying optimal conditions and aircraft design is essential to minimize instability.
Dong et al. numerically investigated the wake flow of the dandelion canopy for different atmospheric conditions using the Large Eddy Simulation.
Because these objects operate on such small scales, they are much more sensitive to atmospheric conditions. At windspeeds of five to ten meters per second, the relative viscous resistance of the seed is high, corresponding to a lower Reynolds number.
“At a low Reynolds number, the wake of the dandelion canopy is relatively ‘pure,’ and the vortex ring structure formed by the downstream reflux area is relatively ‘ordered.’ The vortex ring produced by the canopy, as a large-scale vortex structure, is in a laminar flow state,” said author Zijian Zhang. “However, with an increase in Reynolds number, the ‘ordered’ vortex will gradually develop into ‘disordered’ turbulence, and this evolution process is the key to determine whether dandelions fly steadily and maintain stable flight.”
The effects of other key design features, such as canopy structure, number of spokes, and load capacity, are also examined.
Using the information about flight mechanisms revealed in this simulation, the authors are already working on a dandelion seed-inspired aircraft prototype.
Source: “Transition to turbulence in the wake of dandelion-like spoke disk,” by Yangyang Dong, Yuyang Ni, Kexin Hu, Tongle Zhang, Zijian Zhang, and Yongbin Wang, Physics of Fluids (2023). The article can be accessed at https://doi.org/10.1063/5.0169161 .
