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zephyrus17 September 29, 2010 23:42

Flow Doesn't Conform to Walls
I want to visualise the flow of air through a nozzle situated in a cylinder (laminar entrance through the cylinder, laminar convergence through the nozzle, turbulent exit from the nozzle, wake futher down a cylinder). I've modelled a small nozzle in the middle of a cylinder using loft and then extruding a cylinder to symmetrically to both sides. I can get the flow into the nozzle (from big entrance converging to small exit), and flow through the general cylinder, but when I try to combine them together by using two domains, the flow just ignores the converging walls of the nozzle, and just goes straight. Using one domain gives me the

2 isolated fluid regions were found in domain
error. What am I doing wrong?

ghorrocks September 30, 2010 05:08

The isolated regions error means your mesh is not connected. You need to fix the mesh up so it is connected. You may be able to do this in CFX-Pre, but no guarantees.

You would have to post a picture of what you are talking about for the flow.

kambireddy September 30, 2010 07:13


I had experienced same error....
i am not getting exactly ur prob description. it would be better to say about my problem and rectification
problem: i had two fluid domains which are separated by isolated wall.

Initially i was creating domain for both fluids as one in cfx-pre ? then during solving its giving error same as u. then i asked one of my frnd, he told me that is due to mesh problem. i would agree with him that this also may be due to mesh problem. but my mesh is very fine.
Then i was tried with separate fluid domains and stated giving separate boundary condition, after that problem was resolved.

What i am suggesting you is if u had two fluid regions, take both are diff domains n start work..
i thought of it would work.
Any queries mail me back...

ghorrocks September 30, 2010 18:20

If you get the isolated fluid regions error then you have two sections of mesh (or more) which are not connected. If this is not intentional then you have a meshing error. You can fix it with multiple domains but this is not recommended. Fix the root cause of the problem and generate one contiguous mesh.

kambireddy September 30, 2010 23:39

Dear Glenn Horrocks,

I am Beginner to cfx n icem. i have doubt that u r saying multi domains are not recommended. suppose take example of our nostrils, here two fluid regions are there. Is it any problem by taking both as single domain, start giving BC`s in pre?
Isolated error is resolved by using separate fluid regions in my problem? suppose as u said mesh problem is there, then though u r giving separate domains it has to give that error, but nope! once again i am telling that i am beginner, may be my question is silly, but i am happy to know the resolved problem by someone who had faced same as me...

ghorrocks September 30, 2010 23:51

Use as few domains as possible. If you are modelling two nostrils and the air around it that would be one domain. If you are modelling two nostrils without the air (so they are not connected at all) then split it into two separate models.

Multiple domains should be kept for multiple frames of reference, CHT simulations or other times when the physics of the different domains are different.

kambireddy October 1, 2010 02:49

Thanks a lot Glenn Horrocks...

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