We use the greek letter
to denote the Circulation of the flow (around a closed contour
).
We define the circulation
around an arbitrary closed contour
according to the contour integral
illustrated in the figure above. According to the definition above,
is obtained at a given instant (Eulerian idea). We take a ``snapshot'' of the flow, and compute
according to the equation above. For a different instant, the snapshot of the flow may be different (unsteady flow, for example), so the value of
for the same contour
may be different.
Karl P Burr
2003-07-07