Flat 2D surface immersed in 3D flow, is it possible?
 

Hello everybody.
This is my problem: I need to run a CFD simulation of a ventilation system, and the problem is that an important piece of the system is made from metal sheets. The only really problematic part is a metal sheet caping an extreme of an inlet with one of its edges free, and I cannot avoid its modelling so easily, but if I account for the sheet thickness it would lead to an unnecessary over refinement on that zone and maybe if I do it the run will not converge.
I would like to know if I can represent this sheet as a simple 2D surface, that is a flat shape with no thickness, and then set it as a wall. Both sides of the sheet are wetted by the flow. I plan to use Code_Saturne.
To show better my problem, please look at this picture http://www.absolutely-clean.com/cms_...hood_after.jpg. The sheet I'm referring too is the big square surrounding the extractor system (it's thin, don't get fooled by the bottom part which is a trough). It's not my geometry but rather similar.
Thank you in advance.

César