Niu Peixing, Atkins Michael D, Liu Yanyan, Li Moxiao, Lu Tian Jian, Kim Tongbeum
State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China.
MIIT Key Laboratory of Multifunctional Lightweight Materials and Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China.
Phys Rev E. 2022 Jul;106(1-1):014405. doi: 10.1103/PhysRevE.106.014405.
During descent, a single-winged maple seed (samara) can naturally reach a delicate equilibrium state, stable autorotation, before landing. This article reveals the intrinsic equilibrium of a particular type of samaras in terms of measurable aerodynamic and geometric parameters. To this end, we conducted a series of in situ measurements for the rate of vertical descent (exclusive of crosswind) of an autorotating samara in a natural range of samara sizes and masses. We then extended the range of size and mass by introducing artificial samaras, with discrete mass elements purposely designed to approximate the asymmetrical and nonuniform distribution of mass found with natural samaras. Based on the widened range, a fundamental nondimensional correlation of dynamic pressure and disc loading was generalized, where all stable autorotation descent profiles collapse to a single descent characteristic curve, irrespective of the size and mass of the natural and artificial samara's specimens. Results reveal that for stably autorotating (both natural and artificial) samaras, their terminal descent velocity (expressed as dynamic pressure) and disc loading attained equilibrium at a value that is inversely proportional to the coefficient of lift.
在下降过程中，单翼枫种子（翅果）在着陆前能够自然达到一种微妙的平衡状态，即稳定的自转状态。本文从可测量的空气动力学和几何参数方面揭示了特定类型翅果的内在平衡。为此，我们对一系列自然大小和质量范围内的自转翅果进行了垂直下降速率（不包括侧风）的原位测量。然后，我们通过引入人工翅果来扩展大小和质量范围，这些人工翅果特意设计了离散的质量元素，以近似自然翅果中发现的不对称和不均匀质量分布。基于扩展后的范围，我们归纳出了动压和盘面载荷的基本无量纲相关性，在该相关性中，所有稳定的自转下降剖面都汇聚到一条单一的下降特征曲线上，而与自然和人工翅果样本的大小和质量无关。结果表明，对于稳定自转的（自然和人工）翅果，它们的终端下降速度（以动压表示）和盘面载荷在一个与升力系数成反比的值处达到平衡。
