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S2S Radiation Model at non conformal interfaces

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Old   May 29, 2017, 10:46
Red face S2S Radiation Model at non conformal interfaces
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Hi
I am just new in ansys fluent.

I am simulated a model imported from Solidworks with heat transfert between a fluid (air) with several solid bodies (wood, steel and a glass).

Radiation is the heat source and I a am facing a complicated situation:

_I have first used just "1 part" as the geometry and the model has been meshed as one part. So as boundaries conditions, I had walls and walls shadows BC between fluid and solid bodies; that I all set as "Coupled" to get heat transfert, with the default values (internal emissivity=1, etc)
Then I solved the case using the S2S radiation model.

_Secondly I have used the "explode part" tool at the geometry pannel and fluent created automatically "mesh interfaces" once I opened the "setup" and the calculation has also been resolved using the S2S radiation model.

My problem is that I have a very great differences in temperatures between the two cases. For instance, between: the wall region between air and steel in the first case; and the same region as interface in the second case; the interface temperature is 50°C upper than the wall and wall shadow temperature.

I have read somewhere that S2S has some issue with "non conformal interfaces" but I haven't really understood what this was really about (non conformal interfaces).

I would like to know which results are correct, or what I should do best.
Please, could someone give me an explanation.

(Sorry for my poor english too, I hope that you can understand me).

Last edited by ataoulalim; May 30, 2017 at 02:36.
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Old   May 30, 2017, 08:44
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The first part seems typical, but I don't understand what this second method is.

Conformal interface means that the mesh on both sides are 1-to-1 matching, or that you have one continuous mesh. Often in multi-body meshing, good quality cannot be achieved and regions have their own distinct meshes. You can imagine one side of the interface has 1000 boundary cells on the Fluid side and 10 boundary cells in the solid side (this is a non-conformal mesh).

When the mesh is conformal, data is simply passed across the interface. When the mesh is non-conformal, the data must be interpolated from one side to the other. The interpolation causes some error and for conjugate heat transfer problems, it is more desirable to have a conformal mesh than to have a really fine mesh that is non-conformal.
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Old   May 31, 2017, 12:03
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Thank you very much for this answer.

In the second method, what I have done was to use the "explode part" tool in GEOMETRY.
Before Using this tool, I had 1 Part and 6 bodies; and after using this tool (explode part) I have got 6 parts and 6 bodies.

After meshing that model I have made the remark that at the interfaces between the different bodies, mesh was different. If I reffer to your explaination, I can conclude that these were non-conformal meshes and that I have had bad results from this case due to interpolation error.

Otherwise, the reason why I explode my model in different parts was because of mesh quality requirements. Once exploded the mesh quality was very good.

But I have now another question about the "Interface" boundary Condition.

Normally, before using this BC; I must have Interface_1 and Interface_2 Named Selections and BC on the body_1 and body_2 in contact; then I have to create a "Mesh Interface".
But I have made the remark that this is only possible when I have different parts in the GEOMETRY (In my second model).

When I had only 1 part as geometry (The first model), I tried to use "interface" BC; but When I create The Interface_1 and Interface_2 as "Named selections" I automatically got and error message about "Overlapping mesh"; And I was then obliged to use "Wall" BC between the two bodies in contact.

My question I now to know if there is a way to have conformal mesh interfaces with different parts in the GEOMETRY model (My second model).
Then I would be able to use the "interface" BC in the contact region between two different bodies, and better mesh quality too.

And thank you again for your answer.

Last edited by ataoulalim; May 31, 2017 at 13:14.
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Old   May 31, 2017, 13:17
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I don't know why you are so obsessed with the interface boundary condition. You should have a coupled wall at each of the fluid|solid and solid|solid boundaries unless your mesh is non-conformal.

Parts & bodies doesn't mean anything to Fluent. What you should pay attention to is the number of cell-zones when you try to read in the mesh.
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Old   May 31, 2017, 13:38
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I am not obscessed with the Interface BC.
I am insisting just because if thé mesh quality I got with this model.

Now with what you're explaining me; I have no choice but using the "wall" Boundary Condition.

Thanks again.


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