Streamlines in Code_Saturne etc.

Forgive my ignorance, but I learn CFD by self-study and experimentation.

A couple of questions:

If I make a mesh containing the shape I want to analyse, the model HAS to be connected to the 'outside' world, otherwise Code_Saturne (CS) wont recognize the groups:
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This is a no go:

Works:

What am I doing wrong?
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How do I do an analyses on a 2D mesh? Most of the time I'm only interested in the 2D shape for experimentation.
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How do I create streamlines rather than visualizing the whole mesh? I'm using Ensight Gold format and Paraview for visualization.

Here I've created two slices for better visualization.



Now I know my questions are weak at best, but maybe next semester I have the time to sit down and read a book on CFD cover to cover - right now CFD is just for relaxation amd fun.