City Research Online

Abstract

Flexible wingtip extensions matched to the Cauchy and Reynolds numbers of a peregrine falcon’s primary feather in flight have been tested in differing configurations and compared to rigid ones for reference. The wingtip configurations were attached to the end of a symmetric (NACA 0012) aerofoil and were tested at 5° and 10° angles of attack and Reynolds numbers of and . Time resolved particle image velocimetry (TR-PIV) was used to study the dynamics of the individual vortices. The results show that, at increased angle of attack the configuration with C-type variation of the free length of the winglets is spreading the vorticity into spanwise and vertical directions, generating a circular multi-core vortex arrangement. In contrast, for the case of winglets of the same length (I-type configuration) a continuous vortex sheet is formed which rolls up into a single core, dislocated outboards and upwards from the original tip-vortex location. This remains the case even for larger angle of attack. It is concluded that – besides the known reduction of induced drag – the former configuration is also beneficial for a more rapid disintegration of the tip-vortex in the wake, while the latter shows less instability. This let us speculate that the latter could be relevant for reducing the tip-noise at higher angle of attack such as for Owls, who hunt during night and have adapted to fly silently.

Publication Type:	Article
Additional Information:	This is an open access article distributed under the terms of the Creative Commons CC-BY license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Publisher Keywords:	Slotted wingtip, Bio-inspired, PIV, Vortex, Self-adaptive
Subjects:	T Technology > TA Engineering (General). Civil engineering (General) T Technology > TL Motor vehicles. Aeronautics. Astronautics
Departments:	School of Science & Technology School of Science & Technology > Engineering
SWORD Depositor:	Symplectic Administrator

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