Modulation effect of asymmetric double-layered filaments on aerodynamic performances of idealized pappus models

The pappus of dandelion (Taraxacum mongolicum) seeds is structurally diverse and complex. Some seeds possess multi-layered, asymmetrically distributed pappus filaments, yet the aerodynamics of such configurations remain unexplored. Here, we numerically investigated how streamwise asymmetry in filament distribution influences aerodynamic performance at a particle Reynolds number (Rep) of about 200, using simplified models with double-layered filaments in which each layer contains half of the total filaments. We designed four groups of simulation cases: in each group, one filament layer angle was fixed (0° or 30°) and the other was varied from 0° to 40°. Across groups, increasing the adjustable filament layer angle reduces both the model's drag and the size of the separated vortex ring (SVR) in the wake. The maximum relative reduction, defined as (maximum–minimum)/maximum, reaches up to 19% for drag and 31% for the SVR size. The fixed filament-layer angle strongly influences the maximum reduction in the SVR size but only weakly influences the maximum reduction in drag. Moreover, as the filament-layer angle increases from 0° to 30°, the SVR height-to-width ratio shifts from a nonmonotonic to a monotonic dependence on the adjustable layer angle. With the fixed filament-layer set to 30°, the maximum relative reduction in the height-to-width ratio is approximately 16% when windward-oriented, compared with about 3% when leeward-oriented. Increasing the angle of the leeward-oriented fixed filament layer raises the fraction of viscous drag in the total drag on the pappus model. These results improve our understanding of the diversity and evolutionary dynamics of dandelion populations.