Explanation:
One should note that the concept of irrotationality applies to a
fluid element in a given flow than to flow itself. The flow may
be a vortex where the streamlines are circular, but the fluid
elements should not rotate or distort to make the flow
rotational. In the above demonstration, flow past an aerofoil
is shown. It should be noted that streamlines are distrorted but
the fluid element only translates and does not change
orientation making the flow irrotational.
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