# Modeling a fan rotation/ fan curve in CFD behind a radiator

Hello. I am trying to model a radiator fan in our FSAE car. So I had a question regarding its modeling. I have read this post regarding modeling fan curve. Can we use the same method for modeling our fan without using actual fan geometry?

If yes, I couldn’t find anything regarding meshing in the above-mentioned post (For example, should I give the actual cell zone to the desired geometry or mesh as is).

If no, can we use the momentum zone for the same? If yes, does it accurately model the pressure drop across the fan along with the given acceleration?

The first image shows the inlet of fan (only if we use the first method)

The second image shows the outlet of the fan.

Please correct me if I am wrong regarding the method or the way of using it.

Cheers!!

Hi @HarshR ,

The fan curve functionality is actually a custom boundary condition (you can think of it as a velocity inlet/pressure outlet). In short, it cannot be assigned to a cell zone and you would need an actual boundary to define it.

Looking at the images that you posted: the simulation would likely run, but the rest of the structure is going to act as a wall. There will be one outlet for the fan and one inlet for the fan on the other side. There won’t be any flow going through the side pod to the sides of the fan (if it makes sense).

On your question about momentum source, yes, it can be used to mimic the effects of a fan without having to model the blades. Of course it’s an approximation, but it saves a lot of mesh as you won’t have to capture the details of the blades.

I would expect to see an overall increase in pressure, if you compare the flow upstream to the flow downstream of the momentum source (just like in a fan). The accuracy in this pressure gradient depends on how much accuracy you are looking for. It should give you an idea but it won’t be spot on. After all, different blades may also produce different pressure drops

I’d recommend running some tests on a simple pipe flow with pressure inlet + pressure outlet and a flow driven by a momentum source as an exercise.

Cheers

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