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On the maintenance of an attached leading-edge vortex via model bird alula

Published online by Cambridge University Press:  11 June 2020

Thomas Linehan Open the ORCID record for Thomas Linehan [Opens in a new window]  and
Kamran Mohseni Open the ORCID record for Kamran Mohseni [Opens in a new window]
Thomas Linehan
Affiliation:
Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL32611, USA
Kamran Mohseni*
Affiliation:
Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL32611, USA Department of Electrical and Computer Engineering, University of Florida, Gainesville, FL32611, USA
*
†Email address for correspondence: [email protected]
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Abstract

Researchers have hypothesized that the post-stall lift benefit of bird’s alular feathers, or alula, stems from the maintenance of an attached leading-edge vortex (LEV) over their thin-profiled, outer hand wing. Here, we investigate the connection between the alula and LEV attachment via flow measurements in a wind tunnel. We show that a model alula, whose wetted area is 1 % that of the wing, stabilizes a recirculatory aft-tilted LEV on a steadily translating unswept wing at post-stall angles of attack. The attached vortex is the result of the alula’s ability to smoothly merge otherwise separate leading- and side-edge vortical flows. We identify two key processes that facilitate this merging: (i) the steering of spanwise vorticity generated at the wing’s leading edge back to the wing plane and (ii) an aft-located wall jet of high-magnitude root-to-tip spanwise flow (${>}80\,\%$ that of the free-stream velocity). The former feature induces LEV roll-up while the latter tilts LEV vorticity aft and evacuates this flow toward the wing tip via an outboard vorticity flux. We identify the alula’s streamwise position (relative to the leading edge of the thin wing) as important for vortex steering and the alula’s cant angle as important for high-magnitude spanwise flow generation. These findings advance our understanding of the likely ways birds leverage LEVs to augment slow flight.

JFM classification

Biological Fluid Dynamics: Swimming/flying Wakes/Jets: Separated flows
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 897 , 25 August 2020 , A17
Copyright
© The Author(s), 2020. Published by Cambridge University Press

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References

Alvarez, J. C., Meseguer, J., Perez, A. & Meseguer, E. 2001 On the role of the alula in the steady flight of birds. Ardeola 48 (2), 161–173.Google Scholar
Austin, B. & Anderson, A. M. 2007 The alula and its aerodynamic effect on avian flight. In Proceedings of the ASME International Mechanical Engineering Congress and Exposition, vol. 7: Engineering Education and Professional Development, Seattle, Washington, USA, November 11–15, pp. 797–806. ASME.Google Scholar
Bomphrey, R. J., Nakata, T., Phillips, N. & Walker, S. M. 2017 Smart wing rotation and trailing-edge vortices enable high frequency mosquito flight. Nature 544, 92–95.CrossRefGoogle ScholarPubMed
Brown, R. E. & Fedde, M. R. 1993 Air flow sensors in the avian wing. J. Expl Biol. 179, 13–30.Google Scholar
Carr, Z. R., Chen, C. & Ringuette, M. J. 2013 Finite-span rotating wings: three-dimensional vortex formation with variations with aspect ratio. Exp. Fluids 54, 1444.CrossRefGoogle Scholar
Carruthers, A. C., Thomas, A. L. R. & Taylor, G. K. 2007 Automatic aeroelastic devices in the wings of a steppe eagle Aquila nipalensis. J. Expl Biol. 210, 4136–4149.CrossRefGoogle ScholarPubMed
DeVoria, A. C. & Mohseni, K. 2017 On the mechanism of high-incidence lift generation for steadily translating low-aspect-ratio wings. J. Fluid Mech. 813, 110–126.CrossRefGoogle Scholar
Dickinson, M. H., Lehmann, F. O. & Sane, S. P. 1999 Wing rotation and the aerodynamic basis of insect flight. Science 284 (5422), 1954–1960.CrossRefGoogle ScholarPubMed
Eldredge, J. D. & Jones, A. R. 2019 Leading-edge vortices: mechanics and modeling. Annu. Rev. Fluid Mech. 51, 75–104.CrossRefGoogle Scholar
Ellington, C. P., van den Berg, C., Willmott, A. P. & Thomas, A. L. R. 1996 Leading-edge vortices in insect flight. Nature 384 (6610), 626–630.CrossRefGoogle Scholar
Foth, C., Tischlinger, H. & Rauhut, O. W. M. 2014 New specimen of Archaeopteryx provides insights into the evolution of pennaceous feathers. Nature 511, 79–82.CrossRefGoogle ScholarPubMed
Freymuth, P., Finaish, F. & Bank, W. 1986 Visualization of wing tip vortices in accelerating and steady flow. J. Aircraft 23 (9), 730–733.CrossRefGoogle Scholar
Hubel, T. Y. & Tropea, C. 2010 The importance of leading edge vortices under simplified flapping flight conditions at the size scale of birds. J. Expl Biol. 213, 1930–1939.CrossRefGoogle Scholar
Hunt, J. C. R., Abell, C. J., Peterka, J. A. & Woo, H. 1978 Kinematical studies of the flows around free or surface-mounted obstacles; applying topology to flow visualization. J. Fluid Mech. 86, 179–200.CrossRefGoogle Scholar
Hunt, J. C. R., Wray, A. A. & Moin, P. 1988 Eddies, streams, and convergence zones in turbulent flows. In Proceedings of the Center for Turbulence Research, pp. 193–208. Stanford University.Google Scholar
Ito, M. R., Duan, C. & Wissa, A. A. 2019 The function of the alula on engineered wings: a detailed experimental investigation of a bioinspired leading-edge device. Bioinspir. Biomim. 14, 056015.CrossRefGoogle ScholarPubMed
Jardin, T. 2017 Coriolis effect and the attachment of the leading edge vortex. J. Fluid Mech. 820, 312–340.CrossRefGoogle Scholar
Jardin, T. & David, L. 2014 Spanwise gradients in flow speed help stabilize leading-edge vortices on revolving wings. Phys. Rev. E 90, 013011.Google ScholarPubMed
Lee, S., Kim, J., Park, H., Jabloński, P. G. & Choi, H. 2015 The function of the alula in avian flight. Sci. Rep. 5 (9914), 63–68.Google ScholarPubMed
Lentink, D. & Dickinson, M. H. 2009 Rotational accelerations stabilize leading edge vortices on fly wings. J. Expl Biol. 212 (16), 2705–2719.CrossRefGoogle ScholarPubMed
Lentink, D., Müller, U.K., Stamhuis, E.J., de Kat, R., van Gestel, W., Veldhuis, L.L.M., Henningsson, P., Hedenström, A., Videler, J. J. & van Leeuwen, J. L. 2007 How swifts control their glide performance with morphing wings. Nature 446, 1082–1085.CrossRefGoogle ScholarPubMed
Linehan, T. & Mohseni, K. 2017 Leading-edge flow reattachment and the lateral static stability of low-aspect-ratio rectangular wings. Phys. Rev. Fluids 2, 113901.CrossRefGoogle Scholar
Linehan, T. & Mohseni, K. 2019 Investigation of a sliding alula for control augmentation of lifting surfaces at high angles of attack. Aerosp. Sci. Technol. 87, 73–88.CrossRefGoogle Scholar
Linehan, T. & Mohseni, K. 2020 Scaling trends of bird’s alular feathers in connection to leading-edge vortex flow over hand-wing. Sci. Rep. 10, 7905.CrossRefGoogle ScholarPubMed
Lipinski, D., Cardwell, B. & Mohseni, K. 2008 A Lagrangian analysis of a two-dimensional airfoil with vortex shedding. J. Phys. A 41 (34), 344011.Google Scholar
Mandadzhiev, B. A., Lynch, M. K., Chamorro, L. P. & Wissa, A. A. 2017 An experimental study of an airfoil with a bio-inspired leading edge device at high angles of attack. Smart Mater. Struct. 26 (9), 094008.CrossRefGoogle Scholar
Meseguer, J., Franchini, S., Prez-Grande, I. & Sanz, J. L. 2005 On the aerodynamics of leading-edge high-lift devices of avian wings. Proc. Inst. Mech. Engrs G 219 (1), 63–68.CrossRefGoogle Scholar
Morse, D. R. & Liburdy, J. A. 2009 Vortex dynamics and shedding of a low aspect ratio, flat wing at low reynolds numbers and high angles of attack. Trans. ASME J. Fluids Engng 131, 1–12.Google Scholar
Muijres, F., Johansson, L., Barfield, R., Wolf, M., Spedding, G. & Hedenstrom, A. 2008 Leading-edge vortex improves lift in slow-flying bats. Science 319 (5867), 1250–1253.CrossRefGoogle ScholarPubMed
Okamoto, M. & Azuma, A. 2011 Aerodynamic characteristics at low Reynolds numbers for wings of various planforms. AIAA J. 49 (6), 1135–1150.CrossRefGoogle Scholar
Pérez-Torró, R. & Kim, J. W. 2017 A large-eddy simulation on a deep-stalled aerofoil with a wavy leading edge. J. Fluid Mech. 813, 23–52.CrossRefGoogle Scholar
Raffel, M., Willert, C. E. & Kompenhans, J. 1998 Particle Image Velocimetry. Springer.CrossRefGoogle Scholar
Rival, D. E., Kriegseis, J., Schuab, P., Widmann, A. & Tropea, C. 2014 Characteristic length scales for vortex detachment on plunging profiles with varying leading-edge geometry. Exp. Fluids 55 (1660), 1–8.CrossRefGoogle Scholar
Saffman, P. G. & Sheffield, J. S. 1977 Flow over a wing with an attached free vortex. Stud. Appl. Maths 57, 107–117.CrossRefGoogle Scholar
Sander, A.2018 The role of the alula in avian flight and it’s application to small aircraft: a numerical study. Master’s thesis, University of Groningen, Groningen, Netherlands.Google Scholar
Sanz, J. L., Chiappe, L. M., Pérez-Moreno, B. P., Buscalioni, A. D., Moratalla, J. J., Ortega, F. & Poyato-Ariza, F. J. 1996 An early Cretaceous bird from spain and its implications for the evolution of avian flight. Nature 382, 442–445.CrossRefGoogle Scholar
Soloff, S. M., Adrian, R. J. & Liu, Z. C. 1997 Distortion compensation for generalized stereoscopic particle image velocimetry. Meas. Sci. Technol. 8, 1441–1454.CrossRefGoogle Scholar
Taira, K. & Colonius, T. 2009 Three-dimensional flows around low-aspect-ratio flat-plate wings at low Reynolds numbers. J. Fluid Mech. 623, 187–207.CrossRefGoogle Scholar
Thomas, A. L. R. 2002 Unconventional lift-generating mechanisms in free-flying butterflies. Nature 420 (6916), 660–664.Google Scholar
Videler, J. J. 2005 Avian Flight. Oxford University Press.Google Scholar
Videler, J. J., Stamhuis, E. J. & Povel, G. D. E 2004 Leading-edge vortex lifts swifts. Science 306 (5703), 1960–1962.CrossRefGoogle ScholarPubMed
Warrick, D. R., Tobalske, B. W. & Powers, D. R. 2009 Lift production in the hovering hummingbird. Proc. R. Soc. Lond. B 276, 3747–3752.CrossRefGoogle ScholarPubMed
Widmann, A. & Tropea, C. 2015 Parameters influencing vortex growth and detachment on unsteady aerodynamic profiles. J. Fluid Mech. 773, 432–459.CrossRefGoogle Scholar
Wieneke, B. 2005 Stereo-PIV using self-calibration on particle images. Exp. Fluids 39, 267–280.CrossRefGoogle Scholar
Willert, C. 1997 Stereoscopic digital particle image velocimetry for application in wind tunnel flows. Meas. Sci. Technol. 8, 1465–1479.CrossRefGoogle Scholar
Wojcik, C. J. & Buchholz, J. H. J. 2014 Vorticity transport in the leading-edge vortex on a rotating blade. J. Fluid Mech. 743, 249–261.CrossRefGoogle Scholar
Wong, J. G. & Rival, D. E. 2015 Determining the relative stability of leading-edge vortices on nominally two-dimensional flapping profiles. J. Fluid Mech. 766, 611–625.CrossRefGoogle Scholar
Xia, X. & Mohseni, K. 2013 Lift evaluation of a two-dimensional pitching flat plate. Phys. Fluids 25 (9), 091901.CrossRefGoogle Scholar
Zhang, F. & Zhou, Z. 2000 A primitive Enantiornithine bird and the origin of feathers. Science 290 (5498), 1955–1959.CrossRefGoogle ScholarPubMed