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Flight characteristics and flow structure of the autorotating maple seeds

Abstract

The present study numerically investigated fluid-physical aspects of the autorotative flight of real maple seeds. The flow field and the motion characteristics of the autorotating maple seed were calculated by simultaneously solving the Navier–Stokes equations for the flow field around the seed and its 6-degree-of-freedom (6DOF) motion. The 6DOF simulation of the autorotative flight of the sample maple seed showed that the seed initially experienced a free-fall and a transient period of motion when all motion parameters of the autorotative flight (spinning rate, descent velocity, coning angle, and pitch angle) fluctuated. The sample maple seed then obtained a high spinning rate within a few seconds and entered into a stable autorotation. The motion parameters at the stable period of the autorotative flight predicted by the 6DOF simulation agreed reasonably well with those measured experimentally for maple seeds of same species and similar geometry. The lift was concentrated at the outer span region of the seed, whereas the drag was distributed relatively evenly over the whole span of the seed. The accelerating spinning moment was produced by the mid-span region of the seed. The flow analysis showed that a compact and attached leading edge vortex (LEV) was developed around the seed, and this LEV was possible by the spanwise transport of vorticity and the consequent spanwise spiraling flow. The compact and attached LEV caused a suction pressure distribution on the leeward surface of the seed, which created the high lift and spinning moment for the autorotative flight of the maple seed.

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Acknowledgements

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science (NRF-2016R1A2B1015783), and this work was supported by the National Research Foundation of Korea (NRF) Grant funded by the Korea government (MSIT) (No. 2018R1C1B5086435).

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MHS was involved in methodology, writing—review & editing, supervision, and funding acquisition. DKI was involved in software, validation, visualization, and writing—review & editing.

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Correspondence to Myong Hwan Sohn.

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The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Sohn, M.H., Im, D.K. Flight characteristics and flow structure of the autorotating maple seeds. J Vis 25, 483–500 (2022). https://doi.org/10.1007/s12650-021-00812-9

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  • DOI: https://doi.org/10.1007/s12650-021-00812-9

Keywords

  • Autorotative flight
  • Real maple seeds
  • Numerical simulation
  • 6-degree-of-freedom motion
  • Leading edge vortex
  • Motion parameters