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June 13, 2018, 02:34 |
nutublendedwallfunction
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#1 |
Senior Member
Nejc
Join Date: Feb 2017
Location: Slovenia
Posts: 196
Rep Power: 9 |
Hi.
I noticed the recent addition of nutUBlendedWallFunction to OF1712 but I'm not sure it's what I think it is: Code:
Description This boundary condition provides a turbulent kinematic viscosity condition when using wall functions, based on a blending of laminar sub-layer and log region contributions. I changed nutkWallFunction to nutUWallFunction in simpleFoam/pitzDaily tutorial and RAS model to kOmega but it produces a floating point exception right away. Should I change something else as well? What's the difference between nutk* stuff and nutU* stuff? Thanks! |
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June 13, 2018, 09:24 |
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#2 | ||
Senior Member
Join Date: Jun 2012
Location: Germany, Bochum
Posts: 230
Rep Power: 15 |
Have not used it, but AFAIK blended wall functions can be used for any y+. They work in the laminar, transition and log-layer. nutk are wall functions which use k for approximation and nutU use the velocity at the wall.
In Doxygen this paper is referenced: Quote:
Quote:
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June 13, 2018, 12:36 |
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#3 |
Senior Member
Nejc
Join Date: Feb 2017
Location: Slovenia
Posts: 196
Rep Power: 9 |
This is all very confusing. I found this 'blended' wall function in ESI-CFD version but now I'm looking in OpenFOAM Foundation omegaWallFunction and it also provides some kind of blending.
What's more, the source also says Code:
Recent tests have shown that the standard switching method provides more accurate results for 10 < y+ < 30 when used with high Reynolds number wall-functions and both methods provide accurate results when used with continuous wall-functions. Based on this the standard switching method is used by default. Code:
Description This boundary condition provides a turbulence kinetic energy wall function condition for low- and high-Reynolds number turbulent flow cases. The model operates in two modes, based on the computed laminar-to-turbulent switch-over y+ value derived from kappa and E. Thank you for your effort, I appreciate your help. I'll also read the paper though I'm afraid it'll take some time to grasp all the gory details |
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June 13, 2018, 14:07 |
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#4 | |
Senior Member
Join Date: Jun 2012
Location: Germany, Bochum
Posts: 230
Rep Power: 15 |
This is what I remember from my research some time ago. Someone might be able to correct my if I am wrong.
The wall functions for omega and u_tau as described in the above-mentioned paper (see Eq. 16 and 18) are the blended versions. According to the paper, they can be used independently of the mesh size. Quote:
http://www.tfd.chalmers.se/~hani/kur...nfoamFinal.pdf nut wall functions are used for better estimation at the wall. There is switching for nut in the nutUBlendedWallFunction as explained above. Till now I either used meshes with y+> 30 using wall functions for omega, k and nut or y+<5 where I did not use wallfunctions or only the omegawallfunction. There are some threads here in the forum giving some advice. If I had to make a guess for meshes which vary y+ from 1 to above 30 I would use omegaWallFunction with blended yes, nutUBlendedWallFunction and kqRwallfunction. |
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June 13, 2018, 17:26 |
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#5 |
Senior Member
Nejc
Join Date: Feb 2017
Location: Slovenia
Posts: 196
Rep Power: 9 |
Finally an answer that makes sense. Thank you, this is what I needed.
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June 13, 2018, 21:57 |
a bug in nutUBlendedWallFunction is fixed in dev
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#6 |
Senior Member
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There was a bug in nutUBlendedWallFunction of v1712. Using nutUBlendedWallFunction in simpleFoam/pitzDaily tutorial case will reproduce this error. Zero gradient at the initial state leads to yPlus of zero.
https://develop.openfoam.com/Develop...lus/issues/696 It is fixed in development-version. You can get it from OpenFOAM-plus gitlab. You have to have an account there. https://develop.openfoam.com/Development/OpenFOAM-plus |
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June 14, 2018, 04:07 |
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#7 |
Senior Member
Nejc
Join Date: Feb 2017
Location: Slovenia
Posts: 196
Rep Power: 9 |
Hehe, I never thought I'd find one.
Thanks for the information. I'm currently stuck on Windows with OF4Win from Turbomachinery CFD and I'll also miss the cyclicRepeatAMI BC. Not sure which one I'd miss more. |
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