a problem about interface setting

whyjackeyson · January 28, 2019, 03:33

Dear everyone. For I'm doing a simulation with two components using the continuity source. Thus, I have to define a constraint with one component. However, for I use a multi-block meshing for my model, some interfaces exist. In the setting page for interface boundary details, I can only find the component except for the constraint component. Therefore, the calculation went wrong and I can not get the result I want. What should I do to solve this?

I think it was caused by the interface setting, for I can get a satisfying result with a default meshing in software, which won't bring the interface. Thanks a lot.

ghorrocks · January 28, 2019, 05:14

Please post your output file, an image of your geometry and mesh and the results you are getting - please explain why the results are wrong.

Post these as attachments to the post, please do not link to third party download sites.

whyjackeyson · January 28, 2019, 09:06

The variable composition mixture I chose was C2H6O and water gas mixture and I have define the C2H6O component as constraint. However, in the interface setting, it only has water component but do not have the constraint component.

Gert-Jan · January 28, 2019, 13:03

What do you want to do with the information of the constraint component on the interface?

In principle, CFX solves an equation for the massfraction of water. The massfraction of the contraint is (1 - masssfraction of water). So, if CFX knows one of them, it automnatically knows the other. Otherwise, it becomes overspecified.

In otherwords, your constraint is known, but 'hidden'.

Opaque · January 28, 2019, 13:06

Could you please post a snapshot of the "interface" you are referring to?

whyjackeyson · January 28, 2019, 22:07

Many thanks for your explanation. Actually, I was unable to fully understand or describe the problem I met. I just met something strange, which was caused by interface I thought.
At first, I have done the meshing automatically with tetrahedral mesh, and I could get a satisfying result.

However, when I just used the multi-block method to finish the meshing (only change the mesh to be structural grids with same model and same cfx setting), the result didn't convergence and not good.

For I just used the hexa grids instead of tetra grids with three blocks, something might go wrong in interface. However, I still can not know why and really confused.

ghorrocks · January 29, 2019, 01:01

Your tet mesh is way too coarse to give any meaningful results. You appear to only have 2 elements through the thickness of your device.

Your hex mesh is approaching the resolution where it might work. With all those sharp angles and corners it is going to have lots of big separations and therefore is likely to be tricky to converge. Have you read the FAQ on this? https://www.cfd-online.com/Wiki/Ansy...gence_criteria

January 28, 2019, 03:33	a problem about interface setting	#1
whyjackeyson New Member Jiacheng Wang Join Date: Feb 2017 Posts: 11 Rep Power: 10	Dear everyone. For I'm doing a simulation with two components using the continuity source. Thus, I have to define a constraint with one component. However, for I use a multi-block meshing for my model, some interfaces exist. In the setting page for interface boundary details, I can only find the component except for the constraint component. Therefore, the calculation went wrong and I can not get the result I want. What should I do to solve this? I think it was caused by the interface setting, for I can get a satisfying result with a default meshing in software, which won't bring the interface. Thanks a lot.

January 28, 2019, 05:14		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,932 Rep Power: 145	Please post your output file, an image of your geometry and mesh and the results you are getting - please explain why the results are wrong. Post these as attachments to the post, please do not link to third party download sites. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

January 29, 2019, 01:01		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,932 Rep Power: 145	Your tet mesh is way too coarse to give any meaningful results. You appear to only have 2 elements through the thickness of your device. Your hex mesh is approaching the resolution where it might work. With all those sharp angles and corners it is going to have lots of big separations and therefore is likely to be tricky to converge. Have you read the FAQ on this? https://www.cfd-online.com/Wiki/Ansy...gence_criteria __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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January 28, 2019, 09:06		#3
whyjackeyson New Member Jiacheng Wang Join Date: Feb 2017 Posts: 11 Rep Power: 10	The variable composition mixture I chose was C2H6O and water gas mixture and I have define the C2H6O component as constraint. However, in the interface setting, it only has water component but do not have the constraint component.

January 28, 2019, 13:03		#4
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,952 Rep Power: 28	What do you want to do with the information of the constraint component on the interface? In principle, CFX solves an equation for the massfraction of water. The massfraction of the contraint is (1 - masssfraction of water). So, if CFX knows one of them, it automnatically knows the other. Otherwise, it becomes overspecified. In otherwords, your constraint is known, but 'hidden'.

January 28, 2019, 13:06		#5
Opaque Senior Member Join Date: Jun 2009 Posts: 1,897 Rep Power: 33	Could you please post a snapshot of the "interface" you are referring to?

January 28, 2019, 22:07		#6
whyjackeyson New Member Jiacheng Wang Join Date: Feb 2017 Posts: 11 Rep Power: 10	Many thanks for your explanation. Actually, I was unable to fully understand or describe the problem I met. I just met something strange, which was caused by interface I thought. At first, I have done the meshing automatically with tetrahedral mesh, and I could get a satisfying result. However, when I just used the multi-block method to finish the meshing (only change the mesh to be structural grids with same model and same cfx setting), the result didn't convergence and not good. For I just used the hexa grids instead of tetra grids with three blocks, something might go wrong in interface. However, I still can not know why and really confused.