Dandelion Seeds Adjust for Flight Attitude to Fly Farther

Dandelion seeds disperse as they float through the air, sometimes flying over a kilometer. Previous work focused on the basic flow mechanism surrounding dandelion seed flight but did not account for gusts of wind near the ground, which could alter the flight attitude and aerodynamics.

Qiu et al. examined the flow pattern around the dandelion seed’s pappus, a disk-like structure with a bundle of filaments attached to a seed. The team investigated five model pappus disks with various porosities to see what factors make natural dandelion seeds, which have a high porosity, unique. They modeled the flight at attitude angles from zero degrees to 20 degrees relative to the horizon.

“When there is an angle of attitude, the stable and symmetric recirculating flow structure above the disk will break, which leads to a considerable loss of the drag performance,” said author Fu-Sheng Qiu. “The inclined attitude will produce a horizontal force, and the pappus will also produce a reversed moment to keep the disk from rolling away from the horizontal plane.”

The findings show the pappus structure has the potential to adjust flight attitude and compensate for windy conditions. The porosity of natural dandelion seed’s pappi led to larger horizontal force coefficients, more stability, and longer flights than disks with lower porosities. Revealing these flight dynamics may lead to new types of microaircraft or drones.

Although the pappus is always modeled as a rigid body, the filaments are elastic structures that vibrate. Qiu said how this will affect the flow mechanism and flight performance remains an open question.

Source: “Numerical investigation on the flow characteristics of model dandelion seeds with angles of attitude,” by Fu-Sheng Qiu, Bo-Wen Wang, Yi-Ming Du, and Hui-Yuan Qian, Physics of Fluids (2021). The article can be accessed at https://doi.org/10.1063/5.0069472 .