Cannot find internal face after simulating

Questions and remarks about code_saturne usage
Forum rules
Please read the forum usage recommendations before posting.
Post Reply
Ruonan
Posts: 136
Joined: Mon Dec 14, 2020 11:38 am

Cannot find internal face after simulating

Post by Ruonan »

Dear developers,

Please could you help me with this question:

I am simulating rotating cavity flows, with a stationary vane in the cavity. The mesh is generated in ICEM, and the vane is simplified to an infinitely thin wall (a face).
model with vane.PNG
mesh with vane.PNG
In Code_Saturne, when I run "mesh preprocessing", I can find this mesh part "vane" in the "preprocessor.log" file. They are internal faces, not boundary faces.
preprocessor.log.PNG
Then, In GUI, I went into "Mesh-Boundary zones-Add from preprocessor log". I found this part "vane" won't be added. That's strange. Then I added it manually and specified it as an adiabatic stationary wall. But when I ran the case and went into post-processing, I found this "vane" is not included in the fluid domain.

I tried in ANSYS CFX, CFX can recognize this face. So could you suggest to me, how could I get this internal face working in Code_Saturne?

Many thanks,
Ruonan
Ruonan
Posts: 136
Joined: Mon Dec 14, 2020 11:38 am

Re: Cannot find internal face after simulating

Post by Ruonan »

The mesh, xml and preprocessor.log files are attached. Thank you!

Best regards,
Ruonan
Attachments
preprocessor.log
(10.09 KiB) Downloaded 106 times
setup.xml
(15.52 KiB) Downloaded 121 times
radial_inflow_one_degree_Farthing_1991_11.cgns
(5.53 MiB) Downloaded 99 times
Yvan Fournier
Posts: 4070
Joined: Mon Feb 20, 2012 3:25 pm

Re: Cannot find internal face after simulating

Post by Yvan Fournier »

Hello,

Should this be an internal (fluid) face, or a boundary (thin wall) face ? If 2 faces are topologically identical, code_saturne considers them as an internal face. From your explanation, I would guess the second is correct.

In the first case, it is not accessible through the GUI, but you can still select faces of this groups using the appropriate (interior face instead of boundary face) selection functions. You cannot assign boundary conditions to interior faces though.

In the second case, you need to transform the internal face into 2 boundary faces. This is possible with the GUI in "Mesh Preprocessing/Other/Interior to boundary faces (boundary insertion)".

Best regards,

Yvan
Ruonan
Posts: 136
Joined: Mon Dec 14, 2020 11:38 am

Re: Cannot find internal face after simulating

Post by Ruonan »

Hello Yvan,

Thank you very much for your reply. Yes, I want it to be a boundary (thin wall) face.

Your suggestion is exactly what I needed. Following your suggestion in GUI and after mesh preprocessing, although there was no difference in "preprocessor.log" file, I can find from "listing" file, that the internal face have been transformed to boundary face. Also, I can find this boundary face in post-processing.

Many thanks,
Ruonan
Ruonan
Posts: 136
Joined: Mon Dec 14, 2020 11:38 am

Re: Cannot find internal face after simulating

Post by Ruonan »

Hello Yvan,

Following your kind suggestion, I transformed the internal face "vane" to boundary face in GUI, and can find it in the boundary domain when post-process. But this boundary face seems didn't work as I expected.

As shown below, I set the vane as a rotating wall, with the same rotating speed as two adjacent discs.
Radial inflow model.png
In post-process, when I look at the tangential velocity contour at one constant radius surface between the two discs, I suppose near the rotating vane, there should be boundary layer flows, with solid body rotation speed. But now I can only find boundary layer flow near the disc, but not near the vane. It seems the rotating vane didn't work properly. But we do see some asymmetry in tangential direction, which seems to be influenced by this internal boundary?
Tangential velocity contour.png
Please could you suggest me, how to make this rotating vane work properly? Did I do something wrong, or are there any extra settings needed for setting boundary conditions on boundary faces in the fluid domain?

Best regards,
Ruonan
Ruonan
Posts: 136
Joined: Mon Dec 14, 2020 11:38 am

Re: Cannot find internal face after simulating

Post by Ruonan »

The mesh, xml and preprocessor.log are attached. Thank you Yvan!

Best regards,
Ruonan
Attachments
preprocessor.log
(10.09 KiB) Downloaded 113 times
setup.xml
(15.68 KiB) Downloaded 106 times
radial_inflow_one_degree_Farthing_1991_12.cgns
(5.77 MiB) Downloaded 110 times
Yvan Fournier
Posts: 4070
Joined: Mon Feb 20, 2012 3:25 pm

Re: Cannot find internal face after simulating

Post by Yvan Fournier »

Hello,

I am not sure I see where your "rotating wall" definition is done. If it is a sliding wall, is it in a cs_user_boundary_conditions.f90 ?

In all cases, a rotating wall is probably not enough. It is a good solution if an outside wall is sliding, but will not be enough if part of its movement is orthogonal to the wall (i.e. it only handles the friction terms).

What you would need is to use the turbomachinery model. For this, you mesh needs to be cut in 3 pieces, cut by discs at the top and bottom of the vane.

- This also assumes the walls move with the vane, and the geometry can be described by a rotation sweep in that section.
- If the walls do not move with the vane, you will need to add an opposite rotational sliding velocity to the walls so as to get the correct friction (i.e. the domain moves, but not the walls)
- If the geometry in the vane area cannot be described by a rotation sweep (i.e. the distance between the vane's sides and the walls may vary, meaning the topology varies, than neither the sliding wall not the turbo-machninery option can work. In that case, the closest approach would be to remove the vane wall and use a rotating source term and possibly rotating porosity and head loss representing the vane.

In any case, I do not see how you can expect to get a correct flow in what seems an intrinsincally 3D problem using a mostly 2D mesh.

Best regards,

Yvan
Ruonan
Posts: 136
Joined: Mon Dec 14, 2020 11:38 am

Re: Cannot find internal face after simulating

Post by Ruonan »

Hello Yvan,

Thanks for your reply. It's very helpful and inspiring.

Yes, the vane is a sliding wall, and I defined the rotating speed in cs_user_boundary_conditions.f90.

I agree with you, perhaps I shouldn't use this mostly 2D mesh to expect the 3D flow. I made a new model including a real 3D vane with thickness. I will first try this to see if the results are better.
Model with vane.PNG
Many thanks,
Ruonan
Ruonan
Posts: 136
Joined: Mon Dec 14, 2020 11:38 am

Re: Cannot find internal face after simulating

Post by Ruonan »

Hello Yvan,

Thank you. I tried the 3D model mentioned in the last post, using wall-resolved RANS in Code_Saturne. The results have reasonable agreements with experimental data, also with previous CFX results. The paper used for data validation is also attached here.

Farthing, P.R., Long, C.A. and Rogers, R.H., 1991, June. Measurement and prediction of heat transfer from compressor discs with a radial inflow of cooling air. In 36th ASME, International Gas Turbine and Aeroengine Congress and Exposition.
Saturne results validation.png
Many thanks,
Ruonan
Post Reply