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THE VELOCITY FIELD

The animation of the velocity vector field confirms what has been shown
in the stream function animation.

When circulation is zero, the uniform stream approaching from the
right divides into two symmetric flows, one going over the cylinder, the
other flowing under it. The two flows connect again downstream of the
cylinder. The flow field is symmetric with respect to the *x*
axis. Two fluid particles immediately above and below the upstream
stagnation point travel the same distance around the cylinder and
then meet again at the downstream stagnation point.

When circulation is increased, the stagnation points move towards the
lower half of the cylinder so that the two companion fluid particles
follow different routes to reach the downstream stagnation point.

In particular the fluid particle that travels above the cylinder
makes a longer route with respect to its companion, but it travels fast
enough to arrive at the same time at the downstream stagnation point.