This 2D flow is confined between no-slip walls. On the inlet (left wall), a Poiseuille velocity profile is enforced through a Dirichlet boundary condition. The outlet is handled with a von Neumann zero-gradient condition on the velocity. A cylindrical obstacle is placed in the channel, at half-way between the walls. The Reynolds number, defined with respect to the diameter of the obstacle, is Re=100. In this regime, a time-periodic pattern appears in the wake of the cylinder, known as a Karman vortex street.

Animation: Animated GIF(2.4 Mb)

2D flow past a cylinder