Wrong CFD results - axial fan simulation

Hi, I am new to simScale and this is my 1st project using MRF.
I have created and run model of an axial fan installed in wind-tunnel for CFD simulation. The simulation was completed successfully without any error but the solutions seem to be incorrect…expecting negative inlet pressure since zero pressure was assigned at the outlet.
Could someone take a look at my setup and see why I am getting wrong results?
Thanks in advance.


To me, it feels like the velocity inlet condition that was defined generates a larger volumetric flow rate than the fan can handle. So this becomes a velocity-driven flow, generating larger pressures at the inlet.

What you could do is to replace the velocity inlet boundary condition by a “Pressure inlet”. With this configuration, the flow will be driven by the rotating motion of the MRF zone.


Hi Ricardo,
Have you had a chance to review the project in greater details to see if the model was setup correctly? As I mentioned this is my first simulation and wanted to make sure everything is setup correctly. I will modify the inlet condition and rerun the simulation.
Thanks again

I ran this model using different software with inlet velocity of 0.5 m/s and got about -500 Pa for inlet pressure (not fully converged). So my inlet velocity seems to be realistic. Can you please look into the setup in more detail. Thanks

Hello @hooshsim ,

I still maintain my initial recommendation of running this case with a pressure inlet BC, instead of a velocity inlet. Just so you can see how it looks, I ran one quick test for 300 iterations (not fully converged yet). Here are the velocities at the inlet:

And here is the pressure:

In case you are interested in comparing results between tools, I would highly recommend thoroughly reviewing the setup, making sure everything is the same (materials, geometry, boundary conditions, mrf definition, etc.).


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What pressure value did you specify at the inlet?

I ran two additional cases with different pressure values at the inlet. The solutions are identical. I think there is something wrong with the model. Can you please validate the model?

Hi, I defined a total pressure of 0 Pa for my inlet (which would be the usual approach for an open path, rotating zone-driven flow).

About your second simulation, didn’t you mean to define a total pressure of +400 instead of -400 for the inlet?

Given the total pressure formulation (P_{total}=P_{static}+0.5*\rho*U^2), defining -400 for the inlet is rather unexpected.


I assigned 400 Pa for total Pressure at the inlet and got -0.1 inlet velocity which is wrong in both magnitude and direction. Also the torque value predicted on the blades are not realistic. Can somebody validate the model instead?