Experimental and numerical investigation of the aerodynamic performances of the salsify seed

Wind-dispersed plant seeds exhibit excellent aerodynamic performance. For example, Taraxacum officinale (dandelion) seed achieves long-distance dispersal through its unique pappus structure. However, its micro-scale structure limits the potential for bio-inspired engineering applications. To explore more scalable pappus structures, this study focuses on the Tragopogon sp. (salsify) seed, with a pappus structure similar to the dandelion seed but at larger physical dimensions. Key geometric features of the salsify pappus structure were extracted and abstracted into a porous disk model. Wind tunnel tests and computational fluid dynamics (CFD) simulations were conducted on three comparative models: a dandelion pappus model, a salsify pappus model, and a solid disk model with the same projected area as the salsify pappus. The numerical results were obtained by solving the incompressible steady Reynolds-averaged Navier–Stokes equations with the Spalart–Allmaras turbulence model using Ansys Fluent software platform. Results of wind tunnel tests show that these models can generate separated vortex rings in the airflow. The separated vortex ring formed by the salsify porous model is the largest and most elongated. CFD simulations further validated these findings and revealed that the salsify pappus structure is the most effective model in suppressing reverse flow and smoothing pressure gradients. These merits can reduce wake diffusion and enhance wake stability. This study offers valuable insights for further investigation of the larger-scale pappus structure and provides a novel insight into the bio-inspired applications.