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What is the consequence of using a high-Re turbulence model on a low-Re grid |
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April 28, 2017, 08:30 |
What is the consequence of using a high-Re turbulence model on a low-Re grid
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#1 |
Senior Member
Yuehan
Join Date: Nov 2012
Posts: 142
Rep Power: 13 |
Hi everybody,
We know that the three major variants of the k-epsilon models, the standard k-epsilon, realizable k-epsilon, and RNG k-epsilon model, are all deemed as high-Re models (correct me if I am wrong here). This means that we typically use them on a high-Re mesh, i.e., having y+ = 30 - 120 approximately, together with wall functions. I usually use the following wall functions in OpenFOAM: Code:
k: kqRWallFunction epsilon: epsilonWallFunction nut/mut: nutkWallFunction/mutkWallFunction However, what is the consequence if I use high-Re models on a low-Re mesh, i.e., having y+ = 1 approximately? Does this negatively or positively impact the accuracy of the results? In addition, what types of wall functions (or boundary conditions) should be used when applying high-Re models to low-Re grids? Should I use the following: Code:
k: kLowReWallFucntion epsilon: epsilonLowReWallFunction nut/mut: nutLowReWallFunction/mutLowReWallFunction https://bugs.openfoam.org/view.php?id=1852 So what type of boundary conditions should be used to replace 'epsilonLowReWallFunction'? Thank you. |
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April 28, 2017, 12:44 |
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#2 |
Senior Member
Uwe Pilz
Join Date: Feb 2017
Location: Leipzig, Germany
Posts: 744
Rep Power: 15 |
As far as I understand this: If you use the wall function at a fine mesh the wall functions will be replaced more and more with the "real" thing. You will mention that k and epsilon will get lower and therewith get more and more out of function.
__________________
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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April 29, 2017, 14:17 |
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#3 |
Senior Member
Yuehan
Join Date: Nov 2012
Posts: 142
Rep Power: 13 |
Many thanks! So you think that using high-Re models on low-Re grids with wall functions wil not negatively affect the accuracy?
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April 30, 2017, 01:29 |
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#4 |
Senior Member
Uwe Pilz
Join Date: Feb 2017
Location: Leipzig, Germany
Posts: 744
Rep Power: 15 |
If you don't use wall functions, there should be no negative effects.
__________________
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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April 30, 2017, 10:26 |
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#5 |
Senior Member
Yuehan
Join Date: Nov 2012
Posts: 142
Rep Power: 13 |
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April 30, 2017, 10:38 |
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#6 |
Senior Member
Uwe Pilz
Join Date: Feb 2017
Location: Leipzig, Germany
Posts: 744
Rep Power: 15 |
Don't use walls, use patches. If the solver requires wall function you may choose any of them. They don't matter.
__________________
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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