Consider the stream function defined as[br][center][math]\psi=Uy\left(1-\frac{a^2}{x^2+y^2}\right)[/math][/center][justify][/justify][justify]The resulting flow is shown in the following simulation, with a cylinder of radius [math]a=1[/math] and speed [math]-2\le U\le2[/math].[/justify]