System inside of bigger system

  • Last Post 10 October 2018
  • Topic Is Solved
Gojko posted this 09 October 2018


I am doing simulation from which I wish to get information on how does wind effect on intlet and outlet of jet engine.

On image below I have simplified geometry of jet engine and an idea on how wind flow behaves around it and on the way in it. 

What boundaries should these faces be given so that my system would work? I wanted to use for the inner inlet and outlet either: pressure or mass flow. For the outer inlet I wanted to use velocity-inlet and for outlet atmospheric pressure.


Based on this video:

have tried also with boolean approach but got stuck in Setup since I cannot use Fan option for my application. 


Flow inside of inner box is not important

I guess someone well experienced will solve this in a blink of an eye, but I am struggling with these for days already...

Thank you for your help,


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rwoolhou posted this 09 October 2018

If you're not interested in the flow through the engine then you could remove that volume from the domain, and only solve around the outside. You'd then use a velocity inlet for the wind, velocity inlet (negative velocity) for the jet intake, velocity inlet for jet exhaust and pressure outlet for the downstream outlet. 

If you are interested in the flow in the engine you need to create a multibody part in DesignModeler or use ShareTopology in SpaceClaim. Then set one end or other of the turbine as a fan, or use a source term in the engine volume.

The domain also needs to be much bigger, but I'll leave you to read up on that: CFD & wind tunnel best practices are good for that sort of information.


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kkanade posted this 09 October 2018

As suggested, please use only outer box. To check share topology, you can watch following video. 


If you are new to simulation, I would recommend you to start with some simple pipe flow and other tutorials. 




Gojko posted this 10 October 2018

Thank you for your answers. It solved my problem and now I already face some other. 

Mr. Keyur, you are definitely right, I should do step by step and not waste your time but certain circumstances forced me in this position. 

I will now continue solving my issues on my own but I hope you will not might if I come back with some other questions in coming days.  

Kind regards,


Gojko posted this 10 October 2018


I am facing some strange problems now: 

Error: Divergence detected in AMG solver: pressure correction

Error Object: #f

I assume it is because of >infinitive< vortex that occurs in my flow.

Once again, I am uploading very simple geometry from which I am trying to learn.

Iterations are OK until 10 and than continuity goes up

R (Right): velocity-inlet: 10m/s

L (Left): pressure-outlet: Gauge: 0 Pa



Also I have tried:
-with similar geometry as original post and in that case it works, so I assume boundary conditions are not case of causing problems. 

-with extremely big enclosure it works fine until 20 iterations and at 90 stops with: Error: Divergence detected in AMG solver: x-momentum

Error Object: #f

x is flow direction

 -Doing finer mesh on the  a) edges b)faces which had improved results but still ran continuity to the sky

I found some ideas on using bulk conditions and am still trying to understand them, but do you maybe have any other ideas how to face this problem?

Kind regards