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Old   April 8, 2013, 13:17
Default Stationary rotor shroud
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Rolando Figueiredo
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Hello everyone,

As I have been trying to model the flow within a gas turbine stage, I have had a problem regarding the stationary shroud in the rotor section. In order to model this I've selected the counter-rotating wall option in the turbomachinery set up mode.

Right after I start CFX-Solve Manager, the following error is reported:

+--------------------------------------------------------------------+
| ERROR #002100080 has occurred in subroutine CHECK_NORMV. |
| Message: |
| The specified velocity vector on the boundary patch |
| |
| Rotor Shroud |
| |
| has a significant normal component at one or more faces. One of |
| these face locations is |
| |
| (x,y,z) = ( 2.74655E-02, 4.23893E-02, 1.07949E-01). |
| |
| The angle between the specified velocity and the element surface is|
| 22.822 degrees at this face. This is considered an error because |
| it implies that the mesh is moving. The following are possible |
| reasons for the error message: |
| 1. There is a setup error; for example, an incorrect axis of |
| rotation. |
| 2. There may be a meshing problem; for example, the nodes on a |
| rotating surface might not lie on the surface of revolution. |
| 3. The boundary is curved and the mesh is very coarse. In this |
| case, you may modify the tolerance by increasing the |
| expert parameter 'tangential vector tolerance wall' |
| from its default of 20 degrees. |
+--------------------------------------------------------------------+

What surprises me is that I have previously successfuly conducted a similar computation, only with a corser mesh (no huge difference - 1m, then 2m elements causing the trouble).

Does anyone have any idea about what's going on? To my knowledge, apart from the meshes, all the other settings are exactly the same...

Thank you in advance for your help!
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Old   April 8, 2013, 18:37
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Glenn Horrocks
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The error message is very clear. A bit of your mesh which should have tangential motion has normal motion. This could be a misunderstanding by the user of the setup, it could be a meshing error where a stray element is in there, or it could be the wrong face was selected for a boundary.

Have a look at the XYZ location it specifies and find the error.
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Old   April 9, 2013, 06:29
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Rolando Figueiredo
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I've tried that, the XYZ coordinates lies in the line that defines the blade tip (in the mesh it actually touches the shroud, although I am modelling the shroud as stationary).

I've modeled the part using Solid Works correctly. However, when I assembled the stator-rotor system I did not align them correctly with the axis. Should that be a problem? I believe CFX should be able to automatically detect the axis of rotation, as long as it is parallel to the Y axis (in this case).

Am I wrong at all?

Here's two images of the point in question:

Untitled.jpg

Untitled2.png
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Old   April 9, 2013, 09:09
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Steve Pugh
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You will need to align them properly with the correct axis. If the axis is parallel but not concentric, CFX will not be able to solve. There should only be 1 axis of rotation with a model of this nature, unless i'm misinterpreting the information.
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Old   April 9, 2013, 09:11
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Rolando Figueiredo
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I understand that but then how come the solver worked when I tried the coarser (though equaly positioned) mesh?

Would you happen to know how I could change the axis of rotation either on CFX-Pre or on ICEM? I don't want to go back to solidworks and redo everything!

Thanks for the reply!
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Old   April 9, 2013, 09:22
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When you mention assembling the rotor-stator system but not aligning them correctly, I assume you assembled them in Solidworks. If thats so, you will need to go back to solid works and re-assemble them as concentric. Otherwise, to change the rotation axis, you can edit the settings in the domain in CFX-Pre.
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Old   April 9, 2013, 09:30
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Rolando Figueiredo
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I see. But that means I'll have to redo the whole mesh, since blocking etc...

Oh well, thank you for the help. I'll try the latter option for now. How exactly could I change edit the settings in the domain (in CFX-Pre)? If anyone has any other shortcuts, I'd be glad to hear them!

Thanks again!
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