ABSTRACT
The clap-and-fling mechanism is a well-studied, unsteady lift generation mechanism widely used by flying insects and is considered obligatory for tiny insects flying at low to intermediate Reynolds numbers, Re. However, some aquatic zooplankters including some pteropod (i.e. sea butterfly) and heteropod species swimming at low to intermediate Re also use the clap-and-fling mechanism. These marine snails have extremely flexible, actively deformed, muscular wings which they flap reciprocally to create propulsive force, and these wings may enable novel lift generation mechanisms not available to insects, which have less flexible, passively deformed wings. Using high-speed stereophotogrammetry and micro-particle image velocimetry, we describe a novel cylindrical overlap-and-fling mechanism used by the pteropod species Cuvierina atlantica. In this maneuver, the pteropod's wingtips overlap at the end of each half-stroke to sequentially form a downward-opening cone, a cylinder and an upward-opening cone. The transition from downward-opening cone to cylinder produces a downward-directed jet at the trailing edges. Similarly, the transition from cylinder to upward-opening cone produces downward flow into the gap between the wings, a leading edge vortex ring and a corresponding sharp increase in swimming speed. The ability of this pteropod species to perform the cylindrical overlap-and-fling maneuver twice during each stroke is enabled by its slender body and highly flexible wings. The cylindrical overlap-and-fling mechanism observed here may inspire the design of new soft robotic aquatic vehicles incorporating highly flexible propulsors to take advantage of this novel lift generation technique.
Footnotes
Competing interests
The authors declare no competing or financial interests.
Author contributions
F.K., D.W.M., and A.E.M conceived and designed the experiment. F.K. and D.W.M. carried out experimental work and data analysis. A.E.M. procured and identified the animals. F.K., D.W.M., and A.E.M. wrote the manuscript. All authors approved the final manuscript.
Funding
Funding was provided by a National Science Foundation CAREER grant to D.W.M. (CBET 1846925), a grant from the National Academies of Science Keck Futures Initiative (NAKFI; National Academies of Sciences, Engineering, and Medicine) to A.E.M. and D.W.M., a University of South Florida New Researcher Grant to D.W.M., a University of South Florida Nexus Grant to D.W.M., and a Bermuda Institute of Ocean Sciences Grant in Aid to D.W.M.
Supplementary information
Supplementary information available online at https://jeb.biologists.org/lookup/doi/10.1242/jeb.221499.supplemental
- Received January 8, 2020.
- Accepted June 19, 2020.
- © 2020. Published by The Company of Biologists Ltd
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