Research On Aerodynamic Drag Of Dandelion Seeds And Geometric Structure Optimization

The dandelion seed is known for its passive flight capability delicately mediated by its fluffy pappus comprising～100 radiating filaments.The pappus,being minimalistic on the materials used,could serve to enhance the aerodynamic drag and stabilize the passive flight at low Reynolds numbers(Re)by inducing a vortex ring in the wake.To date,researchers have conducted ample studies on dandelion seeds,and have achieved certain research results.There are no clear design strategies and research ideas for enhancing the aerodynamic drag F_D of dandelion seeds through structural optimization.In this regard,we conducted computational fluid dynamics analysis on the real-sized pappus morphology,and investigated the effects of the number,aspect ratio,and deviation angle of filaments on the aerodynamic drag.We identified that its unique geometric features,specifically,the number(n～100)and aspect ratio(AR～450)of the filaments,are most likely the results of natural evolution that aims to optimize the drag-inducing efficiency.Moreover,inspired by the highly porous and symmetric geometry of the natural dandelion pappus,we first investigated the aerodynamic performance of periodically arranged filaments with infinite lengths and single filaments with finite lengths at different Reynolds numbers.Next,we designed two series of geometric models with parallel and V-shaped configurations,and investigated the effects of different configurations on aerodynamics performance,and we found the“equidistant”configurations could make better use the wall effect than the“V-shaped”counterparts,and thus enhance the drag coefficient C_D and the aerodynamic drag.Finally,in order to take advantage of equidistant configurations to enhance the drag coefficient,we designed a variety of“artificial pappi”featuring equidistance between neighboring filaments,which we confirmed capable of making better use of the“wall effect”in low-Re regime,thus producing even higher drags with no additional material cost.In particular,we present a series of“Archimedean-spiral”configurations,among which the polymeric one(n=100)outperforms the natural radiating pappus in drag induction,yet without significantly compromising the high geometric symmetry and the flight-stabilizing capability characteristic of the latter,as a vortex ring could be recapitulated downstream as effectively.Our work here demonstrates that the dandelion seed(and probably other plumed seeds as well)is an exquisite design that embodies the nature’s genius in subtly balancing minimalism and sophistication,and yet the seed’s aerodynamic performance could be further optimized nonetheless with judicious geometric reconfiguration.Our findings here can also provide optimized cost-effective solutions for the design of miniaturized passive underwater/aerial devices.