OpenFOAM
A good source of information is the user guide:
The tutorials link: http://www.openfoam.org/docs/user/
The download link: http://www.openfoam.org/download/ubuntu.php
GUI for OpenFoam
HELYXOS is Engys’ free-to-download Open Source native GUI for OPENFOAM®.
Jordi Casacuberta Puig OpenFoam Website
Interesting Link
2- Good Tutorial to start from for a flow around a cylinder.
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