Wake structure and wing kinematics: the flight of the lesser dog-faced fruit bat,Cynopterus brachyotis

Tatjana Y Hubel,Sharon M Swartz,Daniel K Riskin,Kenneth S Breuer

doi:10.1242/jeb.043257

Tatjana Y Hubel, Sharon M Swartz + Show 2 more

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https://doi.org/10.1242/jeb.043257

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Abstract

We investigated the detailed kinematics and wake structure of lesser dog-faced fruit bats (Cynopterus brachyotis) flying in a wind tunnel. High speed recordings of the kinematics were conducted to obtain three-dimensional reconstructions of wing movements. Simultaneously, the flow structure in the spanwise plane perpendicular to the flow stream was visualized using time-resolved particle image velocimetry. The flight of four individuals was investigated to reveal patterns in kinematics and wake structure typical for lower and higher speeds. The wake structure identified as typical for both speed categories was a closed-loop ring vortex consisting of the tip vortex and the limited appearance of a counter-rotating vortex near the body, as well as a small distally located vortex system at the end of the upstroke that generated negative lift. We also investigated the degree of consistency within trials and looked at individual variation in flight parameters, and found distinct differences between individuals as well as within individuals.

Highlights

Considerable effort has been expended to gain understanding of force generation by flapping wings
Investigations of manufactured wings and mechanical models inspired by insects and birds provide basic insight into flow conditions and the development of aerodynamic forces over moving wings, only studies of living animals can reveal the actual kinematics and aerodynamics of insect, bird and bat flight
The current study greatly extends the initial demonstration of time-resolved Particle image velocimetry (PIV) by our group (Hubel et al, 2009), providing significantly more detail on the wake vortex structure and kinematics, as well as considerable detail regarding variation between individuals in both kinematics and wake patterns

Summary

Introduction

Considerable effort has been expended to gain understanding of force generation by flapping wings. In addition to PIV, high speed videography has been used to reveal the detailed motion of the wings, providing insight into the motion itself, as well as, in some cases, elastic deformations due to aerodynamic and internal forces These approaches and others have been applied with great success to insect and bird flight in the engineering and biological communities over the last two decades (Dickinson and Gotz, 1996; Ellington, 1999; Usherwood and Ellington, 2002; Sane, 2003; Spedding et al, 2003a; Tobalske et al, 2003; Usherwood et al, 2003; Tobalske et al, 2007)

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