Abstract
To study wing-wake interaction for various wing flexibilities, force measurements and digital particle image velocimetry were carried out on flapping hawkmoth-like wings in a water tank. Wing thickness was employed as a design variable for the wing flexibility distributions. Abrupt flap-down and phase delay in flexible wings influenced the behaviors of the Leading-Edge Vortex (LEV) and Trailing-Edge Vortex (TEV), generated by the previous stroke. While the rigid wing exhibited a detached LEV at the end of the stroke, wing with specific flexibilities obtained attached LEVs. The attached LEVs induced a relatively rapid flow toward the wing surface as a result of encountering the TEV, and the flow caused a higher lift peak. On the other hand, the wings with larger wing deformations generated distinctive changes in LEV and TEV behaviors. The flap-down helped the TEV form closer to the wing surface, and it thus caused a downwash rather than wing-wake interaction. Furthermore, the most flexible wing had a newly-formed pair of LEVs above the wing during the wing reversal, thereby being not able to generate the wing-wake interaction. These results help to understand the different vortex structures generated by flexible wings during the wing reversal and the corresponding effects of wing-wake interaction.
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Acknowledgment
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and future Planning (NRF-2015R1A2A2A 01002536), and was also supported by a National Sciences and Engineering Research Council of Canada (NSERC) grant RGPIN227747-2012.
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Ryu, Y., Chang, J.W., Chung, J. et al. Experimental investigation of flexible hawkmoth-like wings on the wing-wake interaction in hovering flight. J Bionic Eng 15, 139–153 (2018). https://doi.org/10.1007/s42235-017-0011-7
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DOI: https://doi.org/10.1007/s42235-017-0011-7