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First published online September 5, 2008
Journal of Experimental Biology 211, 2909-2918 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.018192
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The near and far wake of Pallas' long tongued bat (Glossophaga soricina)

L. Christoffer Johansson1,*, Marta Wolf1, Rhea von Busse2, York Winter2, Geoffrey R. Spedding3,{dagger} and Anders Hedenström1

1 Department of Theoretical Ecology, Lund University, Sölvegatan 37, SE-223 62 Lund, Sweden
2 Department of Biology, Bielefeld University, D-33501 Bielefeld, Germany
3 Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90098-1191, USA


Figure 1
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  		Fig. 1. Wake velocity and vorticity (s–1) plots of the near wake in the streamwise plane [x, z] for the outer wing (A), inner wing (B) and centre of the body (C) at a flight speed 1.5 m s–1, and in the transverse plane [y, z] at mid-downstroke (D), mid-upstroke (E) and end of upstroke (F) at a flight speed of 4 m s–1. The white arrow indicates the vortex ring generated at the outer wing during the end of the upstroke. Vorticity is scaled according to the colour bar to the right of each row and vectors are scaled according to the reference vector (modified from Hedenström et al., 2007Go).

 

Figure 2
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  		Fig. 2. Definition of the diameter and angle relative to the horizon of the vortex ring generated at the outer wing during the end of the upstroke (see text) as seen in the streamwise [x–z] (A) and transverse [y–z] (B) planes. The small vortices (small orange- and blue-filled circles) represent the outer wing vortex ring. The large circles represent start (orange) and stop (blue) in A and mid-wing vortices in B. The inserted wake models of the near wake at a flight speed of 4 m s–1, as suggested previously (Hedenström et al., 2007Go), show the laser sheet cut through the wake. Blue cross-stream tubes represent start vorticity and red cross-stream tubes stop vorticity. Blue streamwise tubes represent tip vortices and red streamwise tubes root vortices. At the end of the upstroke the outer wing sheds separate vortex rings, shown in dark red.

 

Figure 3
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  		Fig. 3. Composite wake velocity and vorticity (s–1) plots of the near wake in the streamwise plane [x, z] for the outer wing (lz) at flight speeds of 2, 3, 5 and 7 m s–1. At 2 m s–1 the images show double start vortices (white arrows) and a single stop vortex. Vorticity is scaled according to the colour bar to the right of each image and vectors are scaled according to the reference vectors, representing the flight velocity, plotted above each composite plot. The size of the images is indicated by the 5 cm scale bar to the left. The upwash during the upstroke is due to the laser sheet cutting outside the tip vortex.

 

Figure 4
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  		Fig. 4. Composite wake velocity and vorticity plots of the near wake in the streamwise plane [x, z] for the inner wing (lx) at flight speeds of 2, 3, 5 and 7 m s–1. At 2 m s–1 the images show double start vortices (white arrows) and a single stop vortex. For further explanation, see Fig. 3.

 

Figure 5
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  		Fig. 5. Composite wake velocity and vorticity plots of the far wake in the streamwise plane [x, z] for the outer wing (lz) at flight speeds of 5 and 7 m s–1. For further explanation, see Fig. 3.

 

Figure 6
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  		Fig. 6. Composite wake velocity and vorticity plots of the far wake in the streamwise plane [x, z] for the inner wing (lx) at flight speeds of 5 and 7 m s–1. For further explanation, see Fig. 3.

 

Figure 7
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  		Fig. 7. Estimated marginal means from the statistical model (see text). Error bars represent the 95% confidence interval of the estimate and wing positions are outer wing (lz), mid-wing (ly), inner wing (lx) and centre of body (lr). (A) Normalized circulation {Gamma}/Uc of the main start and stop vortices at different wing positions in the near and far wake based on the combined dataset. The means were estimated at a flight speed of U=5.3 m s–1. c, mean chord. (B) Normalized circulation ({Gamma}/Uc) of the main start and stop vortices at different wing positions based on the near-wake data. The means were estimated at U=3.5 m s–1. (C) Circulation of the main start and stop vortices relative to the total circulation ({Gamma}/{Gamma}tot) of the same sense at different wing locations in the near and far wake, based on the combined data set. The means were estimated at U=5.4 m s–1.

 

Figure 8
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  		Fig. 8. Interpretation of the wake in the transverse plane [y–z] at the end of the upstroke (see text) as the wake moves progressively downstream (A–C). Inserted wake models illustrate the evolution of the wake and the cuts through the wake at the different distances downstream of the wing.

 

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© The Company of Biologists Ltd 2008