Aerodynamic analysis of flattened pappus structures with linearly radial changes in filament diameter

Significant advances have been made in understanding the interaction between airflow and dandelion seed pappus models consisting of a central disk and tens of filaments. Previous theoretical analyses and numerical simulations assumed a radially constant filament diameter. However, experimental measurements revealed that the filament diameter could vary radially. The effect of radial variations in filament diameter on the interaction between airflow and dandelion seeds has not yet been explored. This piece of work, therefore, numerically investigated the flow patterns around five flattened pappus models with linearly radial changes in filament diameter and the aerodynamic forces acting on these models, across particle Reynolds numbers from 38 to 603. The vortex size, pressure coefficient and streamwise speed in the wake zones in the xoz plane (The z-axis coincides with the symmetry axis of the pappus structure.), the pressure coefficient, radial speed and streamwise speed in the xoy plane, the drag coefficient of the entire pappus model, and the aerodynamic force acting on a single filament were quantitatively analyzed and compared across the five models. It reveals that the radial change in filament diameter indeed results in the variations in these physical quantities among the five models. The variations can be significantly influenced by the particle Reynolds number, although these physical quantities exhibit different degrees of sensitivity. Our findings here will enhance the modeling of dandelion seed dispersal by wind and aid in optimizing the design of micro aircraft inspired by the architecture of real dandelion seed pappus structures.