SimScale CAE Forum

Fan Pressure BC


#1

Hello, i’m having trouble using the Fan Pressure Boundary condition in the middle of the domain

I want to simulate the effect of the fan. I started with a simple project (fan + a bluff body, just to see if the interaction is realistic).

Simulation "Volume"
At first I thought I had to set an inlet and outlet face of the fan. In this simulation I did that but thos clearly hasn’t worked

Simulation "Superficie"
Then I tried with only a surface but this still gives me strange results.

Maybe I’m getting lost with something very simple but I don’t find any resource with this bc used inside the domain.


#2

Hi @wilove!

Before I go more into depth here, maybe this post from my old colleague can help you out: Custom BC: Fan pressure

Keep us updated!

Jousef


#3

Thank you. I saw that post but in that case the bc is used at the bounding walls of the domain. I need the opposite of that (bc inside the domain).

Maybe it is not possible to do what I’m thinking but up until now I have set the bc without a deep understanding of it. Since there are few resources, I hope this topic can make things clearer.


#4

Are you saying that the results you are getting for Run 4 are not what you expected, if so what did you expect?

Run 4:


#5

Do you think it is realistic?

It seemed to me that it was not for 3 reason:

  1. I expected more uniformity of the p and U field in front of the fan
  2. The filed away from the fan is highly perturbed
  3. The residuals seems high

Maybe this is due to the bad mesh (I did not put too mush effort in it). What do you think?

Furthermore, if it is ok the way I used the BC, the ‘in’/‘out’ setting should be useless (I should get the same results since the face where the BC is applied influence the domain on both sides). Probably I’m wrong but I can’t see why :thinking:


#6

I do not know what the purpose of the internal velocity BC on the fan is…

Why are you ramping the P to the fan with a csv file?

Convergence is not solely determined by low residuals, you need a force or coefficients results on some geometry to verify that those results are stable over a large number of the final iterations.

Besides, your residuals are not anywhere near becoming stable, you need more iterations…

We really need to know what results you are interested in…


#7

I’m doing this simulation only to understand how the bc works. I will use the fan bc coupled with a radiator. Both are placed in a duct and I’m interested in the effect of those in the flow outside the duct.

My aim was to obtain, for this simple simulation, something like this:

From what I read online, I thought that this bc worked using an inlet and and outlet.

  • The mass flow would be the one flowing in the intlet
  • In and Out patch are “connected” with mass conservation and the dP would be calculated according the fan Q-dP curve

Clearly I was wrong but since the radiator+fan will be put inside a conveyor, it is not a problem to reduce the fan as a surface.

I set the velocity BC of the fan patch as “pressure inlet-outlet” since it was suggested in the topic i linked above. Reading the OpenFOAM documentation I think it makes sense.

Probably I’m misinterpreting the question but: simply because that was needed for the bc.

Tomorrow I will perform a simulation with more iterarion, meanwhile envery suggestion is welcome!


#8

I do not think I can be of much help here…

But, now with this further information which you have provided, there will be someone here who can help you further… :pray: