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Fig. 10. (A–E) Smoke visualization of static tethered dragonflies. The
dragonflies are still, and the images represent baseline data showing what the
flow around the dragonflies looks like when they are not flapping. The
successive images step from the right (far) wing hinge across the thorax and
out along the near wing. In (A) the smoke plane is aligned with the far wing
hinge, and smoke flows smoothly past the 5 mm diameter mount below the insect,
becoming incorporated in the Karman street (red arrow) behind the mount far
downstream. The flow over the thorax is attached back to the hinge of the
hindwings, and then separates to form an unstructured wake behind the body. In
(B) the smokeplane is on the midline, and the smoke hits the dragonfly between
the eyes. Below the dragonfly the smoke is entrained into the Karman street
(red arrow) behind the mount support. Smoke streams flowing over the top of
the thorax are attached back to a point behind the forewing hinge, but then
separate as the top surface of the thorax descends towards the abdomen. Flow
above the thorax is essentially linear and undisturbed. Flow behind the thorax
is separated forming an unorganised bluff-body wake. In (C) the smoke
intersects the wing at 1/4 wing length. The wings are stationary, but a Karman
street behind the wings (red arrow), and slight downwards deflection of the
smoke-streams indicates that they are held at some small positive static angle
of attack. The flow below the insect is disturbed by the Karman street behind
the mount support at the far downstream end of the image. In (D) the smoke
intersects the wings at 3/4 wing length. As in (C) the flow over the wings
themselves is attached, but a Karman street (red arrow) behind the trailing
edge shows that the wings are held at some small positive static angle of
attack. The flow is otherwise apparently laminar. (E) Here smoke hits the wing
near the wingtip. The flow pattern remains similar to that seen further
inboard in C and D, with a trailing Karman vortex street (red arrow).
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