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A separated vortex ring underlies the flight of the dandelion

机译：分离的涡流环是蒲公英飞行的基础

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摘要

Wind-dispersed plants have evolved ingenious ways to lift their seeds(1,2). The common dandelion uses a bundle of drag-enhancing bristles (the pappus) that helps to keep their seeds aloft. This passive flight mechanism is highly effective, enabling seed dispersal over formidable distances(3,4); however, the physics underpinning pappus-mediated flight remains unresolved. Here we visualized the flow around dandelion seeds, uncovering an extraordinary type of vortex. This vortex is a ring of recirculating fluid, which is detached owing to the flow passing through the pappus. We hypothesized that the circular disk-like geometry and the porosity of the pappus are the key design features that enable the formation of the separated vortex ring. The porosity gradient was surveyed using microfabricated disks, and a disk with a similar porosity was found to be able to recapitulate the flow behaviour of the pappus. The porosity of the dandelion pappus appears to be tuned precisely to stabilize the vortex, while maximizing aerodynamic loading and minimizing material requirements. The discovery of the separated vortex ring provides evidence of the existence of a new class of fluid behaviour around fluid-immersed bodies that may underlie locomotion, weight reduction and particle retention in biological and manmade structures.
机译：风散发的植物已经进化出巧妙的方法来举起种子（1,2）。普通的蒲公英使用一束增强阻力的硬毛（pappus）来帮助保持种子高高。这种被动飞行机制非常有效，可以使种子在巨大距离内散布（3,4）；然而，支撑巴布斯介导的飞行的物理机制仍未解决。在这里，我们可视化了蒲公英种子周围的流动，发现了一种异常类型的涡流。这个涡流是一个循环流体的环，由于流过巴氏杆菌，该环流分离了。我们假设圆盘状的几何形状和巴氏小孔的孔隙率是能够形成分离的涡流环的关键设计特征。使用微细磁盘对孔隙度梯度进行了调查，发现具有类似孔隙度的磁盘能够概括出丘疹的流动行为。蒲公英巴布斯的孔隙率似乎已被精确调整以稳定涡流，同时最大化空气动力学负荷并最小化材料要求。分离的涡流环的发现为流体浸没物体周围存在一类新的流体行为提供了证据，这可能是生物和人造结构中运动，重量减轻和颗粒保留的基础。

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  • 来源
    《Nature》 |2018年第7727期|414-418|共5页
  • 作者

    Cummins Cathal; Seale Madeleine; Macente Alice; Certini Daniele; Mastropaolo Enrico; Viola Ignazio Maria; Nakayama Naomi;

  • 作者单位

    Univ Edinburgh, Inst Energy Syst, Sch Engn, Edinburgh, Midlothian, Scotland;

    Univ Edinburgh, Inst Mol Plant Sci, Sch Biol Sci, Edinburgh, Midlothian, Scotland;

    Univ Edinburgh, Inst Mol Plant Sci, Sch Biol Sci, Edinburgh, Midlothian, Scotland;

    Univ Edinburgh, Inst Energy Syst, Sch Engn, Edinburgh, Midlothian, Scotland;

    Univ Edinburgh, Inst Integrated Micro & Nano Syst, Sch Engn, Edinburgh, Midlothian, Scotland;

    Univ Edinburgh, Inst Energy Syst, Sch Engn, Edinburgh, Midlothian, Scotland;

    Univ Edinburgh, Inst Mol Plant Sci, Sch Biol Sci, Edinburgh, Midlothian, Scotland;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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