SimScale CAE Forum

Thermal simulation featuring a fan in the middle of the part (i.e., not at a boundary)



This is more of a conceptual question than a specific issue with a specific SimScale project. I have a simulation that consists of a metal box (modelled as a “No-Slip” “Specific Conductance Interface Thermal” Contact between an air solid inside the box and a second air solid extending outside the box; because the walls of the box are very thin), with some heat-generating things inside the box. I want to add a fan inside this sealed box to help distribute the heat around. Here are the options I can think of, along with why they don’t feel suitable:

  • Add “pressure outlet”/“velocity outlet” boundary conditions to a face inside my box: This would be “cheating” because such an outlet would produce air of the pre-specified temperature, which doesn’t model a fan well at all (a fan outputs air at essential the same temperature as at its input.)
  • Simulate a fan using a rotational zones etc: Way too complicated, I have the pressure/flow rate specs of my preferred fan already, I don’t want to remodel the fan from scratch.

What I really want is a way to ‘link’ two boundary conditions together such that there is a prescribed pressure difference between them, and air escaping from the higher-pressure face inherits its temperature from the (average of the) lower-pressure face. Or something like that. But I feel like such functionality is not available? (Yet?)

Any confirmation that this is or isn’t supported, plus any other ideas, would be most appreciated.

My current project is at the link below, but there’s really not much to see because I haven’t added anything to represent the fan yet:


Thanks for your detailed description of your problem!

@CFD-SQUAD, can you give our user some hints on how to “optimally” approach his simulation?




Hummmm, what do you think about using a momentum source? You can set a geometry primitive inside the inner box and it will mimic the effects of a fan.


Hi Jousef & Richard,

Thanks so much; this is exactly what I was looking for!

I have another question on a totally different subject but about the same project here, any ideas there would be most greatly appreciated too.

Thanks again,