Ansys Employee

I would consider using a scale-resolving turbulence model instead of the URANS approach.  Try using the Stress-Blended Eddy Simulation (SBES) model.  You might also include turbulence transition modeling.  Of course, you'll need to have an appropriate mesh proximal to the cylinder with y+~=1 and 10-15 inflation layers in the boundary layer.  Using this approach allows for reasonable prediction of the Strouhal number, so it should be appropriate for your FSI application.