It must  be said that one of the most important problems in fluid mechanics is that of flow separation.
It is highly nonlinear, inherently  unsteady in nature.
It is no surprise that it is one of the most heavily studied phenomena in fluids.

A direct numerical simulation of linearly sheared flow past a circular cylinder has been performed. A second-order accurate finite volume scheme is used to integrate the
unsteady Navier-Stokes equations.  However, turbulent models of Fluent solver are not adapted to such a phenomenon.
The results performed have been obtained with artificials boundaries conditions ; The outflow sides have made appear the first three vortices of the Von Karman street but
in an opposing view the momentun loss does not allow us to see more than this three vortices.

Therefore, to have better results, some part of the numerical model have to be modified:
- perhaps the meshing.
- boundaries conditions more pertinents.
- an adapted turbulent model.