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how to set the boundary layer in openfoam?

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Old   May 15, 2014, 05:30
Question how to set the boundary layer in openfoam?
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Wen Yuan
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Hi,

I'm simulating the flow around cylinder,and I need to set a fixed length to the cylinder patch so that it can be suitable for y+. But I don't know how to do it in openfoam, could anybody can help me??

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WenY
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Old   May 16, 2014, 05:34
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Dear Weny,

there are several options to get your boundary layer.

  • If you use blockMesh for your cylinder you can play around with your ratio settings (please have a look into the UserGuide -> Section blockMesh)
  • If you use snappyHexMesh you have to activate the layer addition part (addLayer true)
  • There is also a tool in the toolbox openfoam which give you the ability to refine the cells near the wall. Only working if you have a pure hex mesh, otherwise your quality will be very bad due to splitted cells
  • Doing it with Salome. This software give you the geomtric part to set up a very nice hex mesh for cyclinders (simple and easy) but you have to know how to mesh it in a correct way


Hope it is helpful.
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Old   May 18, 2014, 22:36
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[QUOTE=Tobi;492290]Dear Weny,

there are several options to get your boundary layer.

  • If you use blockMesh for your cylinder you can play around with your ratio settings (please have a look into the UserGuide -> Section blockMesh)
QUOTE]
Dear Tobi,

Thanks for your help. I use the blockMesh for my cylinder, But playing around with ratio settings can not get a fixed distance to the cylinder
, I wanna have a fixed y+, so what can I do?

Best Regards,
WenY
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Old   May 18, 2014, 22:37
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Quote:
Originally Posted by Tobi View Post
Dear Weny,

there are several options to get your boundary layer.

  • If you use blockMesh for your cylinder you can play around with your ratio settings (please have a look into the UserGuide -> Section blockMesh)
  • If you use snappyHexMesh you have to activate the layer addition part (addLayer true)
  • There is also a tool in the toolbox openfoam which give you the ability to refine the cells near the wall. Only working if you have a pure hex mesh, otherwise your quality will be very bad due to splitted cells
  • Doing it with Salome. This software give you the geomtric part to set up a very nice hex mesh for cyclinders (simple and easy) but you have to know how to mesh it in a correct way


Hope it is helpful.
Dear Tobi,

Thanks for your help. I use the blockMesh for my cylinder, But playing around with ratio settings can not get a fixed distance to the cylinder
, I wanna have a fixed y+, so what can I do?

Best Regards,
WenY



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Old   May 19, 2014, 09:51
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Tobias Holzmann
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Quote:
Originally Posted by WenY View Post
Dear Tobi,

Thanks for your help. I use the blockMesh for my cylinder, But playing around with ratio settings can not get a fixed distance to the cylinder
, I wanna have a fixed y+, so what can I do?

Best Regards,
WenY



Hi Weny,

y+ is estimated on the first cell heigth and depend also on velocity. If you have different velocitys you will get other y+ values. Can you explain your problem with a picture?

That would be very recommended and other people can help you in a more specific way.
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Best regards,
Tobias Holzmann

Some interesting OpenFOAM tutorials, publications and videos on www.Holzmann-cfd.de
OpenFOAM Beginners should check out the new wiki on wiki.openfoam.com
A list of some active OpenFOAM contributers can be found »here«
A book about the basics of »Mathematics, Numerics, Derivations and OpenFOAM« can be found on www.Holzmann-cfd.de
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Old   May 19, 2014, 22:11
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here is my model

I used different ways to mesh my model, but get different results of the dragcoeff. I want to know whether the results is related to the mesh condition, or something else?
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Old   May 19, 2014, 22:30
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Quote:
Originally Posted by Tobi View Post
Hi Weny,

y+ is estimated on the first cell heigth and depend also on velocity. If you have different velocitys you will get other y+ values. Can you explain your problem with a picture?

That would be very recommended and other people can help you in a more specific way.
Hi Tobi,

I'm sorry the picture may fail to upload, I just try it again.
There is another problem in my simulation: when I used blockMesh to mesh the model, the result was reasonable, But when I used gambit to mesh, the result was wrong. I guess it might be the cause of a wrong boundary or intial conditions.https://www.dropbox.com/s/4yx55pnwi8...t-cylinder.pdf

It's really very kind of U to help me!
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