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Unsteady dynamics of rapid perching manoeuvres

  • Delyle T. Polet (a1), David E. Rival (a1) (a2) and Gabriel D. Weymouth (a3)


A perching bird is able to rapidly decelerate while maintaining lift and control, but the underlying aerodynamic mechanism is poorly understood. In this work we perform a study on a simultaneously decelerating and pitching aerofoil section to increase our understanding of the unsteady aerodynamics of perching. We first explore the problem analytically, developing expressions for the added-mass and circulatory forces arising from boundary-layer separation on a flat-plate aerofoil. Next, we study the model problem through a detailed series of experiments at $\mathit{Re}=22\,000$ and two-dimensional simulations at $\mathit{Re}=2000$ . Simulated vorticity fields agree with particle image velocimetry measurements, showing the same wake features and vorticity magnitudes. Peak lift and drag forces during rapid perching are measured to be more than 10 times the quasi-steady values. The majority of these forces can be attributed to added-mass energy transfer between the fluid and aerofoil, and to energy lost to the fluid by flow separation at the leading and trailing edges. Thus, despite the large angles of attack and decreasing flow velocity, this simple pitch-up manoeuvre provides a means through which a perching bird can maintain high lift and drag simultaneously while slowing to a controlled stop.


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Baik, Y., Bernal, L., Granlund, K. & Ol, M. 2012 Unsteady force generation and vortex dynamics of pitching and plunging aerofoils. J. Fluid Mech. 709, 3768.
Berg, A. M. & Biewener, A. A. 2010 Wing and body kinematics of takeoff and landing flight in the pigeon (Columbia livia). J. Expl Biol. 213, 16511658.
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 (23), 41364149.
Carruthers, A. C., Thomas, A. L. R., Walker, S. M. & Taylor, G. K. 2010 Mechanics and aerodynamics of perching manoeuvres in a large bird of prey. Aeronaut. J. 114 (1161), 673680.
Doyle, C. E., Bird, J. J., Isom, T. A., Johnson, C. J., Kallman, J. C., Simpson, J. A., King, R. J., Abbott, J. J. & Minor, M. A.2011 Avian-inspired passive perching mechanism for robotic rotorcraft. In IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2011, pp. 4975–4980.
Garmann, D. J., Visbal, M. & Orkwis, P. D. 2013 Three-dimensional flow structure and aerodynamic loading on a revolving wing. Phys. Fluids 25, 034101.
Green, P. R. & Cheng, P. 1998 Variation in kinematics and dynamics of the landing flights of pigeons on a novel perch. J. Expl Biol. 201 (24), 33093316.
von Kármán, T. & Sears, W. R. 1938 Airfoil theory for non-uniform motion. J. Aeronaut. Sci. 5, 379390.
Maertens, A. P. & Weymouth, G. D. 2015 Accurate Cartesian-grid simulations of near-body flows at intermediate Reynolds numbers. Comput. Meth. Appl. Mech. Engng 283, 106129.
McCroskey, W. J. 1982 Unsteady airfoils. Annu. Rev. Fluid Mech. 14 (1), 285311.
Milne-Thomson, L. M. 1968 Theoretical Hydrodynamics, 5th edn. Macmillan.
Moore, J., Cory, R. & Tedrake, R. 2014 Robust post-stall perching with a simple fixed-wing glider using LQR-trees. Bioinspir. Biomim. 9 (2), 025013.
Ol, M. V., Bernal, L., Kang, C. K. & Shyy, W. 2009 Shallow and deep dynamic stall for flapping low Reynolds number airfoils. Exp. Fluids 46, 883901.
Pierrehumbert, R. T. 1980 A family of steady, translating vortex pairs with distributed vorticity. J. Fluid Mech. 99 (1), 129144.
Pitt Ford, C. W. & Babinsky, H. 2013 Lift and the leading edge vortex. J. Fluid Mech. 720, 280313.
Provini, P., Tobalske, B. W., Crandell, K. E. & Abourachid, A. 2014 Transition from wing to leg forces during landing in birds. J. Expl Biol. 217, 26592666.
Raffel, M., Willert, C., Wereley, S. & Kompenhans, J. 2007 Particle Image Velocimetry: A Practical Guide, 2nd edn. Springer.
Reich, G., Wojnar, O. & Albertani, R. 2009 Aerodynamic performance of a notional perching MAV design. In Proceedings of the 47th AIAA Aerospace Sciences Meeting, American Institute of Aeronautics and Astronautics. Article ID: 2009-63.
Saffman, P. G. & Szeto, R. 1980 Equilibrium shapes of a pair of equal uniform vortices. Phys. Fluids 23 (12), 23392342.
Theodorsen, T.1935 General theory of aerodynamic instability and the mechanism of flutter. NACA Tech. Rep. 496.
Wagner, H. 1925 Über die Entstehung des dynamischen Auftriebes von Tragflügeln. Z. Angew. Math. Mech. 5 (1), 1735.
Weymouth, G. D. & Triantafyllou, M. S. 2012 Global vorticity shedding for a shrinking cylinder. J. Fluid Mech. 702, 470487.
Weymouth, G. D. & Triantafyllou, M. S. 2013 Ultra-fast escape of a deformable jet-propelled body. J. Fluid Mech. 721, 367385.
Weymouth, G. D. & Yue, D. K. P. 2011 Boundary data immersion method for Cartesian-grid simulations of fluid–body interaction problems. J. Comput. Phys. 230 (16), 62336247.
Wibawa, M. S., Steele, S. C., Dahl, J. M., Rival, D. E., Weymouth, G. D. & Triantafyllou, M. S. 2012 Global vorticity shedding for a vanishing wing. J. Fluid Mech. 695, 112134.
Xia, X. & Mohseni, K. 2013 Lift evaluation of a two-dimensional pitching flat plate. Phys. Fluids 25, 091901.
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Unsteady dynamics of rapid perching manoeuvres

  • Delyle T. Polet (a1), David E. Rival (a1) (a2) and Gabriel D. Weymouth (a3)


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