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Old   March 14, 2019, 06:48
Default Interface between rotating and stationary
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Iljar Dickhof
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Hello all,

I'm trying to model an impeller which rotates in an air box while being connnected to an inlet-vent. In this model I've tried te make a rotating fluid domain for the impeller which rotates in the air box (stationary fluid domain). I've set the frame change option for the interface between stationary and rotational to "Frozen Rotor". Then an error occurs which says:

"the Pitch change option 'Automatic' is not valid if side 1 or 2 of the interface has a 360 degree or greater pitch angle, ..."

I now know something is wrong with the interface between the rotating domain and the stationairy domain and when i'm trying to solve this problem it fails immediately.

Does anyone know how to solve this problem? What do I need to fill in for Pitch change or do I need to make a different interface with different options between stationary and rotational?

Greetings,

Iljar Dickhof
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File Type: png Situatie simulatiemodel.PNG (45.6 KB, 21 views)
File Type: jpg Knipsel2.jpg (80.6 KB, 17 views)
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Old   March 15, 2019, 03:03
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urosgrivc
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Yes, the answer is:

Do not put all Contact surfaces under one interface.
make two or more interfaces, and put faces which have Constant radial dimension in one interface and surfaces which have fixed axial direction in the second connection.
And you can select pitch change, none, if it doesn't affect your simulation (This one is probably the culprit)
Please provide feedback if it worked.

Last edited by urosgrivc; March 15, 2019 at 04:14.
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Old   March 15, 2019, 03:49
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You should actually use pitch change none! We recently had a case where CFX internally decided that it was some wrong value (with automatic setup) and results were unreasonable. For cases when you model all 360 of the rotating interface, this is the way to go I think.
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Old   March 15, 2019, 08:14
Default Error 2
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Iljar Dickhof
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Hallo all,

First of all, thanks for responding. You're the best!

Secondly, I splitted the interface of the rotor in more interfaces: 3 interfaces for rotor to box and 1 interface for rotor to inlet. All interfaces have for pitch change "none" selected. I also compressed the air box because it wasn't necessary to be this big. It led unfortunately to more errors (image 1).

In the first image it says the pitch change can only by "none" if the interface between face 1 and 2 perfectly match. I think it has something to do with the mesh connection between these faces, correct me if i'm wrong. My mesh can be seen in image 2.

Does anyone know how i perfectly align the faces or is there another solution which i'm not seeing.

Note: It has nothing to do with the direction of the interfaces (axial or radial) as can be seen in image 3, where the same error occurs as in image 1.

I would like to hear from you.

Greetings,

Iljar
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File Type: png Mesh.PNG (125.5 KB, 22 views)
File Type: jpg Error 4.jpg (69.7 KB, 15 views)
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Old   March 15, 2019, 08:24
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You do have perfectly matching faces, so dont worry about this one just select none and you can leave it as it is
yellow exclamation point is not a fatal error, cfx is just making sure that you know what you are doing

The Red X, now that is the problem though, that needs to be solved

Last edited by urosgrivc; March 18, 2019 at 02:15.
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Old   March 15, 2019, 10:18
Default Error Fixed
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Iljar Dickhof
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Well, i restarted cfx-pre again and the red error disappeared. I don't know why... I did manage to get some results (see images) so I think my problem is fixed.

Thanks for the help!
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File Type: png Result 2.PNG (127.0 KB, 12 views)
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Old   March 18, 2019, 02:20
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My recommendation to improve your simulation is only this;
that you make the mesh better at the interface, it is best if the mesh is conformal at the interface, if this is not possible (like for transient rotor-stator) than it is good if the mesh size on both sides of the interface is the same.
this is not necessary but is much better

Last edited by urosgrivc; March 18, 2019 at 06:23.
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