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discontinuity of solution due to interfaces ?

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Old   December 20, 2010, 05:07
Default discontinuity of solution due to interfaces ?
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Hi Foamers,
I am trying to do a couette cell type flow with a small gap at the bottom
I used a wedge-type 5 geometry.
I have a problem at the interfaces since i divided my geometry into 3 different blocks attached at the interfaces (see the attached file)

I got a discontinuity in the velocity profile.
Look at the attached files pleeeeeeease
Help ?

thanks a lot

T.D.
Attached Files
File Type: zip couette-bottom_gap.zip (79.4 KB, 8 views)
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Old   December 20, 2010, 08:41
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Felix L.
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Hello, T.D.,


your mesh is much too coarse at the interfaces. In y-direction you have a jump in cell height of factor 10 or more! Refine your mesh at the interfaces so the cell heights increase with a maximum factor of 2.

Greetings,
Felix.
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Old   December 20, 2010, 09:43
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hi
thanks for your reply
but i did not understand how i must do it, since it is a wedge and obliged not to mesh in y - direction.
so what i shall do?
execuse me but i'm not expert with meshing and with blockMesh
any simple ideas (solution) quickly?

thanks a lot

yours,

T.D.
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Old   December 20, 2010, 10:19
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Felix L.
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Hey,


for a tutorial about using blockMesh please have a look at the lid-driven cavity tutorials. Also this link may provide some help, too.

Yes, you're right, I was mixing the y axis and the z axis. Your mesh needs more grading in the z and x direction at the interfaces. You also need to resolve the gradients at the walls by using grading. Please search for basic meshing tutorials to get some information about that. The blockMesh tutorial also has some information about grading.

You'll find a screenshot attached of what I mean by reducing the cell size ratio at the interfaces. It's just a basic setup, qualitatively showing the way it should be. You've got to find out the required number of cells and growth ratios by yourself.

This is the blocking definition I used to create that grid:

Code:
blocks
(
hex (0 11 10 0 9 4 3 9) (20 1 15) simpleGrading (0.1 1 0.5)
hex (11 2 1 10 4 13 12 3) (25 1 15) simpleGrading (3 1 0.5)
hex (4 13 12 3 8 6 5 7) (25 1 35) simpleGrading (3 1 30)
);
Good luck,
Felix.
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File Type: jpg grid.jpg (27.3 KB, 12 views)
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Old   December 20, 2010, 10:42
Default Thanks a lot
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ah Ok, i got it now
Thank you so so much

yours,

T.D.
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