Time-varying wing-twist improves aerodynamic efficiency of forward flight in butterflies

• Published in: PloS one Vol. 8; no. 1; p. e53060
• Main Authors: Zheng, Lingxiao, Hedrick, Tyson L, Mittal, Rajat
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 16.01.2013; Public Library of Science (PLoS)
• Subjects: Aerodynamics; Analysis; Animals; Biology; Biomechanical Phenomena - physiology; Butterflies; Butterflies & moths; Butterflies - anatomy & histology; Butterflies - physiology; Camber; Computational fluid dynamics; Computer applications; Computer simulation; Deformation; Deformation effects; Engineering; Flapping wings; Flexibility; Flight; Flight, Animal - physiology; Fluid; Fluids; Forward flight; Insects; Kinematics; Mathematical models; Mechanical engineering; Models, Biological; Morphology; Navier-Stokes equations; Organ Size; Orthoptera; Reproducibility of Results; Stokes flow; Studies; Three dimensional flow; Time Factors; Wings; Wings, Animal - anatomy & histology; Wings, Animal - physiology; Maryland; Baltimore Maryland
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0053060

Insect wings can undergo significant chordwise (camber) as well as spanwise (twist) deformation during flapping flight but the effect of these deformations is not well understood. The shape and size of butterfly wings leads to particularly large wing deformations, making them an ideal test case for investigation of these effects. Here we use computational models derived from experiments on free-flying butterflies to understand the effect of time-varying twist and camber on the aerodynamic performance of these insects. High-speed videogrammetry is used to capture the wing kinematics, including deformation, of a Painted Lady butterfly (Vanessa cardui) in untethered, forward flight. These experimental results are then analyzed computationally using a high-fidelity, three-dimensional, unsteady Navier-Stokes flow solver. For comparison to this case, a set of non-deforming, flat-plate wing (FPW) models of wing motion are synthesized and subjected to the same analysis along with a wing model that matches the time-varying wing-twist observed for the butterfly, but has no deformation in camber. The simulations show that the observed butterfly wing (OBW) outperforms all the flat-plate wings in terms of usable force production as well as the ratio of lift to power by at least 29% and 46%, respectively. This increase in efficiency of lift production is at least three-fold greater than reported for other insects. Interestingly, we also find that the twist-only-wing (TOW) model recovers much of the performance of the OBW, demonstrating that wing-twist, and not camber is key to forward flight in these insects. The implications of this on the design of flapping wing micro-aerial vehicles are discussed.