2D expansion pipe boundaries

12366636 · April 12, 2016, 07:41

Hey all,

I have a problem trying to set up periodic boundaries.

I have an expansion pipe that I am trying to model the radius of.

The slice that I have used to model the radius is 1 element thick.

The centre is set to symmetric and I am trying to set the sides as rotational periodicity.

Here are the pictures of the geometry, periodic conditions and the error that I get in solver.

http://imgur.com/a/2F3bF

Thanks,

Eddie.

ghorrocks · April 12, 2016, 08:25

The error message in the output file is very clear, tells you exactly what the problem is and what you need to do about it. The text starts with "All verticies for a fluid domain lie on boundaries..."

I think your problem is that you are modelling a translationally periodic domain, not a rotationally periodic domain. If you want a rotationally periodic domain you need to have a wedge, not a linear extrusion and you need 2 or more elements thick.

12366636 · April 12, 2016, 09:19

Hey Glenn,

Thanks again for helping me.

I did wonder if the rotational periodicity would cause a problem.

I have changed the periodicity to translational and am still getting an error.

http://imgur.com/a/V8Tq3

I then changed the thickness of my mesh to 2 elements thick to see if this was causing the problem.

The simulation now seems to be working fine!

Thanks again,

Eddie.

12366636 · April 12, 2016, 09:40

Hey,

Thanks for all your help.

I was wondering if you could give me some advice about this 2D expansion pipe problem.

I would like to look at the development of the flow at intervals of 5 iterations, at the moment I running it at every 5 iterations and then taking a screenshot.

Is there a way that I can set CFX to take snapshots at every few iterations and save the results?

This would be much easier and less time consuming than doing it manually.

Thanks,

Eddie.

ghorrocks · April 12, 2016, 21:44

Look in the backup files of the results tab on CFX-Pre. You can set regular backup files there.

12366636 · April 14, 2016, 10:30

Sorry Glenn,

I've ran the simulation creating a backup file every iteration.

How can I view these backups?

Thanks,

Eddie.

ghorrocks · April 14, 2016, 19:53

Load them in CFD-Post

April 12, 2016, 07:41	2D expansion pipe boundaries	#1
12366636 New Member Eddie Join Date: Mar 2016 Location: Great Britain Posts: 10 Rep Power: 10	Hey all, I have a problem trying to set up periodic boundaries. I have an expansion pipe that I am trying to model the radius of. The slice that I have used to model the radius is 1 element thick. The centre is set to symmetric and I am trying to set the sides as rotational periodicity. Here are the pictures of the geometry, periodic conditions and the error that I get in solver. http://imgur.com/a/2F3bF Thanks, Eddie.

April 12, 2016, 09:40	Flow development	#4
12366636 New Member Eddie Join Date: Mar 2016 Location: Great Britain Posts: 10 Rep Power: 10	Hey, Thanks for all your help. I was wondering if you could give me some advice about this 2D expansion pipe problem. I would like to look at the development of the flow at intervals of 5 iterations, at the moment I running it at every 5 iterations and then taking a screenshot. Is there a way that I can set CFX to take snapshots at every few iterations and save the results? This would be much easier and less time consuming than doing it manually. Thanks, Eddie.

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April 12, 2016, 08:25		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	The error message in the output file is very clear, tells you exactly what the problem is and what you need to do about it. The text starts with "All verticies for a fluid domain lie on boundaries..." I think your problem is that you are modelling a translationally periodic domain, not a rotationally periodic domain. If you want a rotationally periodic domain you need to have a wedge, not a linear extrusion and you need 2 or more elements thick.

April 12, 2016, 09:19		#3
12366636 New Member Eddie Join Date: Mar 2016 Location: Great Britain Posts: 10 Rep Power: 10	Hey Glenn, Thanks again for helping me. I did wonder if the rotational periodicity would cause a problem. I have changed the periodicity to translational and am still getting an error. http://imgur.com/a/V8Tq3 I then changed the thickness of my mesh to 2 elements thick to see if this was causing the problem. The simulation now seems to be working fine! Thanks again, Eddie.

April 12, 2016, 21:44		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	Look in the backup files of the results tab on CFX-Pre. You can set regular backup files there.

April 14, 2016, 10:30		#6
12366636 New Member Eddie Join Date: Mar 2016 Location: Great Britain Posts: 10 Rep Power: 10	Sorry Glenn, I've ran the simulation creating a backup file every iteration. How can I view these backups? Thanks, Eddie.

April 14, 2016, 19:53		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	Load them in CFD-Post