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May 18, 2017, 03:26 |
Wall functions vs. boundary layers
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#1 |
Senior Member
Nejc
Join Date: Feb 2017
Location: Slovenia
Posts: 196
Rep Power: 9 |
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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May 18, 2017, 03:51 |
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#2 |
Senior Member
Uwe Pilz
Join Date: Feb 2017
Location: Leipzig, Germany
Posts: 744
Rep Power: 15 |
> 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.
__________________
Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950) |
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May 18, 2017, 04:09 |
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#3 |
Senior Member
Nejc
Join Date: Feb 2017
Location: Slovenia
Posts: 196
Rep Power: 9 |
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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June 12, 2017, 08:05 |
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#4 |
Senior Member
Nejc
Join Date: Feb 2017
Location: Slovenia
Posts: 196
Rep Power: 9 |
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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Tags |
boundary cells, boundary conditions, boundary layer, wall boundary condition |
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