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Wall functions vs. boundary layers

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Old   May 18, 2017, 02:26
Default Wall functions vs. boundary layers
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Hello,

I am a bit confused about wall functions and meshes with layers on walls.

If I understand correctly, wall functions model boundary layer of the flow near the wall so it applies to first layer of cells in mesh. Those cells must be thicker than y+.

If I make a mesh with layers on walls thinner than y+ there is no need for wall functions because conditions in boundary layer are calculated directly.

Suppose I have a mesh from the latter case. What boundary conditions should I set for k and omega? What's the 'omega' value on the wall? Infinity?

How do I estimate y+ in a pipe?
The calculator (https://www.cfd-online.com/Tools/yplus.php) requires boundary layer length. What length should I use, say, for a very long pipe?

Thanks!
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Old   May 18, 2017, 02:51
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> What boundary conditions should I set for k and omega?

There is no need to set any wall functions in your case. Simply set a no-slip boundary condition at the walls.
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Old   May 18, 2017, 03:09
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I can't do that. I can set a noSlip BC for velocity but there's no such thing for k and omega. There is an omega BC called 'slip' but that's definitely not 'noSlip'
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Old   June 12, 2017, 07:05
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A few more questions.

When calculating y+, I need boundary layer length. What does that even mean? I have fully developed flow at the inlet, so what length should I choose?
I'm trying to simulate a centrifugal pump.
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boundary cells, boundary conditions, boundary layer, wall boundary condition

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