SimScale CAE Forum

Nozzle Simulation boundary condition


I’m trying to perform a nozzle simulation. This is my project.

My problem is that when I post-process my results I see that the outlet boundary condition is not respected (considering the velocity).
I think that my bc are a bit messy but I don’t precisely know what is wrong.

(In addition: can you please confirm me that I’m using a correct turbolence model? The flow outside the nozzle is more steady than I expected)


Hi @lv_wilove!

If you want to use “Nozzle” you have to make sure that the geometry is completely closed (we call this watertight) then you won’t have the artifact as in your project where a box is build around your object. Once that has been done you will be able to perform an internal flow analysis.

Also consider using symmetries in these simulations if you want, an example can be found here: Compressible Laval Nozzle Simulation.

Regarding turbulence models, this doc might help:




Thank you very much for the fast response and for the simulation reference! That is a great help.

My problem is that my nozzle is only convergent, therefore I want to simulate external expansion right outside the efflux section.

I set up my geometry like that because the alternative I imagined was this:

I thought that in the agles the results would have been not very close to the reality.

Am I wrong?
What do you suggest?


Hi @lv_wilove!

But then you still need to make sure the outlet is closed, it is a necessity if you want to perform flow analyses - you can set atmospheric conditions for the outlet if that suits your case. @CFD-SQUAD, what do you think here?




Ok. I’ve tried with the geometry that I’ve shown in the second message. I’m still completely stuck! I’m getting the error " Maximum number of iterations exceeded": I’ve tried to troubleshoot the problem with SimScale guide but I had no success.

I’ve no idea how to solve errors with this simulation. Do you have some suggestions?


Tagging my mate @Get_Barried here who has done more compressible simulations than I did. Barry do you think he can succeed with a mesh like that? I would also make use of rotational symmetries as mentioned in post number two.