Problem with open vent

[Swissi]

Hi everyone,
I''ve a problem in setting an open vent at the top of a room (to allow the smoke to go out).
When I set the vent (Open surface), the smoke is not going out.
I suppose I''ve a problem with the mesh boundaries but I don''t really understand what to do.
I''ve just set a normal mesh.

What do I have to do? Thanks a lot!!

[Charlie Thornton]

It would be best if you could post your FDS input file - then we can probably tell you exactly what is going on.

Otherwise:

- When you run the simulation, is FDS printing any errors or warnings about VENTS?
- How did you make your open VENT? The way I like to open the top is by right-clicking the MESH (in the tree), then selecting the Open Mesh Boundaries option. That will add hidden open vents to all six sides and you can delete any open vents you don''t want.

[Swissi]

Hello Charlie,
Thanks for your answer!

I think I resolved the problem. Indeed, I didn''t well understand the principle of open mesh boundaries options. I read it in the FDS user guide but I didn''t understand the concept. Could someone please help me? 

[Charlie Thornton]

I don''t think I can say it any better than the FDS users guide. From section 7.4.2 (Special Vents):

...it denotes a passive opening to the outside. By default, FDS assumes that the exterior boundary of the computational domain (the XBs on the MESH line) is a solid wall. To change this, use an OPEN vent as if it were an open door or window.

That section goes on to describe what parameters control the environment beyond the open vent.

What part is giving you trouble? If you aren''t comfortable with how FDS is doing the solver calculations across the VENT, you might want to check out the technical reference. If it''s something else, maybe we can help.