Wake flow visualization of a dandelion pappus with posture change

Abstract

A typical plant that is distributed by wind is the dandelion, which possesses a complex hairy pappus that aids in flying. A pappus or group of bristly filaments found in plumed seeds is believed to have a role in drag enhancement. The pappus prolongs the descent of the seed. For wind-dispersed seeds, maintaining stability while reducing falling speed in turbulent winds may be useful for long-distance dispersal. However, it is unclear why plumed seeds chose a bristly pappus over a membrane that resembles wings and is known to increase lift during passive flight. In the current study, we analyze the dandelion pappus flight mechanism by identifying the crucial structural elements that enable its stable flight. In addition, we investigate the flow behavior around the pappus by performing float testing on several dandelion pappi in a vertical airflow pipe. The flow fields in the wake of the pappus were also measured by 2-component particle image velocimetry. The falling speed of the pappus is reliant on the posture during free-fall motion, and the aerodynamic features of the pappus are substantially affected by the posture in flight. The pappus’s posture was changed to promote vortex growth in the wake, and this vortex behavior is related to the fluid forces acting on the pappus.