[cheye]

I am trying to simulate flow through two concentric pipes using an axisymmetric 2D simulation (not periodic).

The first difficulty is that the inner pipe is only half as long as the outer and neither end extends to the inflow nor outflow of the whole domain. Thus, I need to define an internal wall zone, but I would like to define it as infinitely thin and avoid removing material from the domain. I have tried sketching lines and making them "edges" of a sort, but they do not appear in the Meshing software and I am left with a simple rectangular domain.

The second issue may be solved in the same way, but I need to define a region within the inner pipe in which to apply a fan model in FLUENT. I understand how to implement the fan model, but it requires defining a zone in the geometry.

If someone can help me with imposing non-intrusive lines on the geometry for meshing purposes, I would greatly appreciate it. Thank you!