[paolo lazzarini]

Dear friends, my name is paolo and I am new italian user, new to CFD but not new to other kinds of numerical simulations (mainly FE with ANSYS and NASTRAN), that I use to run for living

I have a problem to set-up with Fluent (trying to learn a bit of CFD) and maybe someone can put me on the right way. I made lots of tutorial here and there but I'm still in the steepest part of the learning curve.

Here a sketch


The problem (it is a real problem that I need to solve at work) is the following.
There is a big mirror of a telescope (it is about 1 m in diameter) that is placed inside a dome at ambient temperature. The mirror is installed into its steel cell and it is initially warmer than ambient (as well as the cell)... I have to study the cooling-down process (transient, but this is not the problem, maybe).

There's a set of fans under the mirror, installed on the steel mirror cell, with a nominal flow rate. These fans are used to help cooling down the mirror before observing. So there's forced convection in between the mirror and the cell plus natural convection around. There's also conduction and blablabla, but I'm focused on forced convection now.

The air is everywhere , around the mirror (in the big dome) and also trapped in between mirror and cell. The so called "dome" where the mirror is immersed is huge...
My problem is: how can I set the correct boundary condition at level of the FANs (that is their nominal mass flow rate) if the fans themselves are not on the boundary but in the middle of a unique "air volume". In other words, I don't have any "named selection area" on which to put a flow rate...

I'm not interested in solving the "fluid features" generated by a really rotating fan, it is just a relatively rough energy/temperature problem made more complex by forced convection...

I was thinking to split the "air" into two different "air zones" in "contact" (the trapped air and the rest of the air) but I don't know how to set this operatively in FLUENT. I was trying with a sort of "interface condition" between two volumes of air but had no success...

Please let me know if the question is well posed and if someone can help me.

My best regards, paolo lazzarini