Vortex wakes of a flapping foil
has in his Ph.D. project made an experimental study of
vortex shedding and wakes of a foil with periodic pitching
oscillations in a two-dimensional free stream created by a flowing
soap film. The flapping foil is a simple realization of a model fish
and the setup makes it possible to study generic features of vortex
shedding with relevance for swimming and flying.
The setup allowed the visualization of both the vortex formation and
the wake evolution and made it possible to make a systematic wake map
in the frequency and amplitude plane and to determine the transition
from von Kármán vortex streets, usually associated with drag, to
inverted von Kármán vortex streets, usually associated with thrust.
The figure below shows a time-series of the vortex formation leading
to a wake in which two vortex pairs are shed in each flapping period.
Vortices are shed both at the round leading edge and at the sharp
trailing edge of the foil. Such wake structures are common behind
Last change: 29 October 2009