Aerodynamic effects of flexibility in flapping wings
- 19 August 2009
- journal article
- Published by The Royal Society in Journal of The Royal Society Interface
- Vol. 7 (44), 485-497
- https://doi.org/10.1098/rsif.2009.0200
Abstract
Recent work on the aerodynamics of flapping flight reveals fundamental differences in the mechanisms of aerodynamic force generation between fixed and flapping wings. When fixed wings translate at high angles of attack, they periodically generate and shed leading and trailing edge vortices as reflected in their fluctuating aerodynamic force traces and associated flow visualization. In contrast, wings flapping at high angles of attack generate stable leading edge vorticity, which persists throughout the duration of the stroke and enhances mean aerodynamic forces. Here, we show that aerodynamic forces can be controlled by altering the trailing edge flexibility of a flapping wing. We used a dynamically scaled mechanical model of flapping flight (Re≈ 2000) to measure the aerodynamic forces on flapping wings of variable flexural stiffness (EI). For low to medium angles of attack, as flexibility of the wing increases, its ability to generate aerodynamic forces decreases monotonically but its lift-to-drag ratios remain approximately constant. The instantaneous force traces reveal no major differences in the underlying modes of force generation for flexible and rigid wings, but the magnitude of force, the angle of net force vector and centre of pressure all vary systematically with wing flexibility. Even a rudimentary framework of wing veins is sufficient to restore the ability of flexible wings to generate forces at near-rigid values. Thus, the magnitude of force generation can be controlled by modulating the trailing edge flexibility and thereby controlling the magnitude of the leading edge vorticity. To characterize this, we have generated a detailed database of aerodynamic forces as a function of several variables including material properties, kinematics, aerodynamic forces and centre of pressure, which can also be used to help validate computational models of aeroelastic flapping wings. These experiments will also be useful for wing design for small robotic insects and, to a limited extent, in understanding the aerodynamics of flapping insect wings.Keywords
This publication has 44 references indexed in Scilit:
- Photogrammetric reconstruction of high-resolution surface topographies and deformable wing kinematics of tethered locusts and free-flying hoverfliesJournal of The Royal Society Interface, 2008
- When wings touch wakes: understanding locomotor force control by wake–wing interference in insect wingsJournal of Experimental Biology, 2008
- A computational investigation of the three-dimensional unsteady aerodynamics ofDrosophilahovering and maneuveringJournal of Experimental Biology, 2007
- Locomotion with flexible propulsors: I. Experimental analysis of pectoral fin swimming in sunfishBioinspiration & Biomimetics, 2006
- Aquatic wing flapping at low Reynolds numbers: swimming kinematics of the Antarctic pteropod,Clione antarcticaJournal of Experimental Biology, 2005
- The role of drag in insect hoveringJournal of Experimental Biology, 2004
- Approaches to the structural modelling of insect wingsPhilosophical Transactions B, 2003
- Computational Biological Fluid Dynamics: Digitizing and Visualizing Animal Swimming and FlyingIntegrative and Comparative Biology, 2002
- Smart Engineering in the Mid-Carboniferous: How Well Could Palaeozoic Dragonflies Fly?Science, 1998
- The aerodynamics of hovering insect flight. II. Morphological parametersPhilosophical Transactions of the Royal Society of London. B, Biological Sciences, 1984