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[Other] how to set the boundary layer in openfoam?

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Old   May 15, 2014, 06:30
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??

Best Regards'
WenY
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Old   May 16, 2014, 06:34
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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, 23:36
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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, 23:37
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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, 10:51
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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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Old   May 19, 2014, 23:11
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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, 23:30
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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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Old   November 1, 2020, 10:13
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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.
Thanks a lot. I am extracting a part of the background mesh to identify it as a solid region using toposet. Of course the mesh for the extracted solid will be the same as that of the background mesh, is it any way possible to add layers from this solid which grow into the the background mesh (identified as fluid) ?

thanks a lot
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