Abstract-
In this presentation, we shall discuss studies of fundamental vortex
interactions, concerned with the dynamics and instabilities of counter-rotating
and co-rotating vortex pairs, coming from wings or generated from flapping
plates. Our DPIV measurements of growth rate for the long-wavelength "Crow"
instability of a counter-rotating vortex pair, coming from delta wing trailing
vortices, or shed from flapping plates, represents the first time that
experimental growth rates have been compared with the theory of Widnall et al.
(1971), without ad-hoc assumptions, yielding good agreement (Leweke &
Williamson, 2002; Miller & Williamson, 2003). We discover a symmetry-breaking
phase relationship for the short-wave instability (Leweke & Williamson, JFM,
1998), which we find to be a "cooperative" elliptic instability. Investigations
of the co-rotating vortex pair show the physical mechanism for vortex merging.
By employing a decomposition of the complete vorticity field, we discover that
the antisymmetric vorticity field comprises two counter-rotating vortex pairs,
which readily push the co-rotating vortex centroids together (Cerretelli &
Williamson, JFM, 2003).
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