jet fan with discharge angle

[fds_user]

Hi,

I'm modeling jet fan with angular component at the discharge side. I'd like to model jet fan with about 5 degree deflecting vanes at the discharge side.

Jet Fan section of the user manual recommends:

You may also want to construct a shroud around the fan using four flat plates arranged to form a short

passageway that draws gases in one side and expels them out the other. The obstruction representing the fan

can be positioned about halfway along the passage (if a louvered fan is being used, place the fan at the end

of the passage).

Form the sensitivity runs, I found out jet fan performance is reduced when the fan is placed at the end of the shroud passage.

Case 1 and 2 have jet fan outlet at the end, and Case 3 has jet fan outlet in the middle. Case 3 resulted in higher airflow the room than other cases with outlet at the end.

I'd prefer to put the fan to be at the end to have clear path of discharge without hitting the shroud wall, but I don't want to lose any jet fan performance.

What is the best way to model jet fan with deflecting vanes? 

Thanks.

[dr_jfloyd]

If you want to have jet be non-orthogonal to the grid, the only real approach to do that is  have the vent be at the discharge side and apply a tangential component to it (see the discussion of louvers in the HVAC writeup in the  User's Guide).

From your sensitivity runs, how do you know which modeling approach best represents reality?  Have you compared against test data?

[Erik Carlsson]

I agree with what dr_jfloyd said.  In addition I also recommend running a couple of sensitivity cases with varying grid cell sizes to ensure your assigned tangential component is adequately resolved.  I have found that with jet fans with angled discharge, I tend to have to use a refined mesh compared to what I would typically use for a fire situation.  Otherwise the modelled tangential component may not reflect the assigned tangential component.