SimScale CAE Forum

Flow rate inlet velocity

Hi everybody!

A quick question.

When setting a boundary condition for the velocity in m3/s i’m not 100% positive if the volume metric flow rate is evenly divided by the area across all selected faces? Or is every face set to the value you set.

As far as i found the documentation does not say anything about selecting multiple faces.


4 faces as inlet with different area’s however the total volumetric flow of all the inlets combined is say 5 m3/s

Can i select all 4 faces and say volume flow rate = 5 m3/s?
Or will that mean that each individual face is set to 5 m3/s?


Hello @STR,

actually the volumetric flow rate is applied on all assigned faces with the absolute defined value. In case you assigned multiple faces to the bc it will therefore add up to a higher flow rate value in total, e.g. three faces with 5 m³/s add up to a total flow rate of 15 m³/s introduced into the domain.
If you want to distribute the total value dependent on the face area of the different inlet faces, you need to first calculate the surface area e.g. with your CAD tool and then set the different flow rates per face accordingly. I noted down that the documentation did not help you on this topic. We will add it there, otherwise it might be confusing or at least not clear!

Thanks for reporting this.

Best Alex

1 Like

Thanks @afischer,

Now my results make a lot more sense. I was scratching my head why i had these high velocities.

I will divide the total flow rate per ratio of the surface area. If you could add that to the documentation it will be clear to others as well.

Have a nice weekend!