JEB desktop wallpaper calendar 2016

Journal of Experimental Biology partnership with Dryad

Wake structure and wing kinematics: the flight of the lesser dog-faced fruit bat, Cynopterus brachyotis
Tatjana Y. Hubel, Daniel K. Riskin, Sharon M. Swartz, Kenneth S. Breuer

SUMMARY

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.

FOOTNOTES

  • Present address: Structure and Motion Laboratory, Royal Veterinary College, Hatfield AL9 7TA, UK

  • Present address: Department of Biology, City College of the City University of New York, New York, NY 10031, USA

  • This work was supported by the Air Force Office of Scientific Research, monitored by Rhett Jeffries, Willard Larkin and John Schmisseur, and the National Science Foundation.

  • Supplementary material available online at http://jeb.biologists.org/lookup/suppl/doi:10.1242/jeb.043257/-/DC1

  • LIST OF ABBREVIATIONS

    A
    area
    ax
    horizontal acceleration
    az
    vertical acceleration
    b
    span of one wing
    c
    wing chord
    dmin
    minimum distance between body and wing tip
    dt
    time between images
    dtnew
    time used to correct for Doppler shift
    f
    wingbeat frequency
    h
    height
    k
    reduced frequency
    Re
    Reynolds number
    SR
    span ratio
    T
    wingbeat period
    U
    free-stream (wind tunnel) velocity
    UB
    speed of bat, relative to test section
    Ut
    total air speed of bat, UUB
    V1
    tip vortex
    V2
    near body vortex
    V3
    positive distal vortex
    V4
    negative distal vortex
    αg
    geometric angle of attack
    β
    stroke plane angle
    βG
    dimensionless height (βG=h/b)
    Γ
    circulation
    ΓAt
    circulation based on total area right of body position
    θtip
    amplitude of wing tip
    ν
    kinematic viscosity
    ρ
    air density
    σ
    standard deviation
    τ
    downstroke ratio
    ω
    vorticity
  • View Full Text