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Fig. 13. Smoke visualizations stepping across the thorax of Aeshna grandis
in tethered flight. The flow pattern, shape, size and structure of the LEV is
consistent at all positions across the thorax, and from wingbeat to wingbeat.
(A–L) Oblique front views in which the dragonfly is traversed through
the smoke plane in 1 mm steps from the far wing hinge across the thorax and
out onto the near wing. There is a leading edge vortex in all images, and the
shape and size of the LEV is consistent across the thorax and out onto the
wing. (I-VI) Higher resolution side images. The dragonfly is traversed through
the smoke plane in 2 mm steps so that the smoke impinges on the far side of
the thorax in I, is on the midline and hits the dragonfly between the eyes in
IV, and is out on the near wing base in VI. The blue arrows show the
stagnation point where the separatrix touches down on the top of the thorax or
hindwing. The shape and size of the leading edge vortex are strikingly
consistent, even though the wing chord and velocity change dramatically as we
step along the wing, across the narrow wing base onto the thorax. This is a
remarkable result, suggesting that while the wings form the LEV the details of
their shape, size and motion are not amongst the principle parameters
controlling LEV morphology.
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