Past exam of the mathematics course of the University of Cambridge / 2014 / ib / Paper 2 / 7B / ii

Here $u=-y$, $v=x$. The streamlines are $x^2+y^2=\text{constant}$. This is rigid rotation counterclockwise with angular velocity one; the origin is a stagnation point and all other trajectories are circles. The middle panel shows their orientation.