This set of simulations consists of 4 simulations that use the same geometry and mesh, but different values of the kinematic visosity $\mu$, and thus achieving different values for the Reynolds number in accordance with its definition: $Re=UD/\mu $.

Flow around a cylinder and the phenomenae that occur at various values of Re is a well known canonical case in fluid mechanics. I did theese simulations to solidify what i learned about CFD and get some practice in OpenFOAM. I ran simulations at Re values of: 1, 20, 55 and 100. The following image found in this paper ilustrates the resulting phenomenae.

Because of the simplicity of the geometry, I constructed it and its mesh using just BlockMesh. I divided the mesh into regions in the way shown in the picture below.

I used the icoFoam solver for all of the cases. The discretization schemes i used are fairly standard and can be found in the fvsSchemes dictionary. The same can be said for fvSolution. I used Scotch decomposition to split the domain into 8 parts and ran the simulations on my AMD FX-8320 CPU which were completed in reasonable time (less than 20 minutes for each).

I visualized the results with the following animation which presents one seceond of the simulations with the first 0.1 seconds playing in a slower speed.

The resulst are as expected. For the lowest Reynolds number there is no backflow. In the case in which the Reynolds number was 20 a steady backflow appears. At the Reynolds number of 55, we can see unsteady shedding of the flow, and at 100 we can see a fully devoloped Karman street.

I also made an animation of the case with a reynold's number of 100 with particle tracing added on.