SimScale CAE Forum

Ventilation through fans inside a Box with openings

Good evening Forum

I have a project, that I am working on, it’s a so called hushbox, a box with a projector in it and internal fans for the cooling.
Now the actual design I currently have is flawed, the projector gets too hot and I wanted to simulate some ideas for improvement.

There is an inlet of air, then a labyrinth with acoustic “barriers” and 6 fans inside and on the other side again an air outlet.

Now my question is, is this even possible to achieve? Acually I want to simulate a conjugate heat transfer, but I am not even able to assign velocity outlets to the fans inside the box. I get a warning “Multiple boundary condition or interface assignments for the following entities: face122@Part 1, face68@Fan, face68@Fan, more” and am not sure if I am on the right track or if the simulation I want to achieve is even possible.

I would appreciate a hint in which direction I should search into getting my knowledge up to speed better.

Thanks and have a nice evening

This is the seemingly erroneous parts. However they are not directly connected. The fans are separated by a rubber Element from the wall.

Ah, and I assigned Air to the square fans (square as I wanted to test a simulation first before I build the fans more realisticly and round).


The project currently doesn’t contain a complete simulation setup, so it’s difficult to know for sure what the settings were. However, from your description, it feels like you were defining boundary conditions to contact faces (which is forbidden, i.e. this page).

If you’re looking to set internal fans for CHT, currently the way to go are momentum sources. You can remove the internal fan volumes from your CAD model and set momentum sources instead.


Thank you for your Tipp Ricardo! I’ll read about this momentum Source, sounds quite about what I need.
I’ll try this tomorrow and will share my experience.

Thanks and good evening

Thank you so much for the tipp!
I had some trouble to find out that I need to add the Material Air to the Volumes which represent the ventilators, but now everything seems to simulate.
The simulation is running now, if that is successful, I’ll build the full model to make some tests.

Thanks again for your help.

Cheers Mav

The simulation aborts again, with a following errormessage:

  • Maximum number of iterations exceeded when calculating temperature from a thermodynamic potential. This may be caused by low-quality mesh producing unrealistic pressure in a few cells or inappropriate boundary conditions, fluid properties or time step. Inspect fields for large values in the last time step.

Now I am not sure, what I am doing wrong. I have created the finest mesh I could. I have set the two holes in the box to natural convection inlet/outlet with 22.5°C, set the temperature inside the box to 22.5°, set the fans inside to momentum sources with (hopefully the correct axis), I have assigned the fluids and solids.

is the model just too complex and I need to increase the maximum runtime? it says that I need 80 core hours for the run. and actually, I just want to test if I have set up everything correctly :slight_smile:

Thanks and cheers

If anybody wonders, I ended up creating geometry primitives inside the air-area to add the speeds. then it worked flawlessly and the model coul dbe calculated.