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-   -   wall functions.-E value, epsilon calculation (https://www.cfd-online.com/Forums/openfoam-solving/63326-wall-functions-e-value-epsilon-calculation.html)

 Xabi April 5, 2009 05:40

wall functions.-E value, epsilon calculation

Hi all!

I am reading through the wall functions code for OF and comparing it with fluent and I noticed some strange things:

1- For the value E instead of using 9.781 as fluent 9 is used.

2- When OF calculates the epsilon for the wall function uses the following formula:
epsilon_[faceCelli] +=Cmu75*pow(k_[faceCelli], 1.5)/(kappa_.value()*RASModel::y_[patchi][facei]);
In Fluent the same formula is used but what is bothering me is the faceCelli term. In fluent epsilon_ is calculated at the point (epsilonp), however, in OF the term epsilon_[faceCelli] seems to refer to the value at the wall.

Xabi

 svens September 10, 2009 13:57

Hey Xabi

I'm also interested how OF is dealing with the wall functions.

So far I'm not really deep in it but about the E thing I found out that they overwriting the E=9 to E=9.8 in the respective turbulence Model with this autoCreateEpsilon (-Nut etc.) function.

Cheers,
Sven

 sven September 11, 2009 18:54

Hey Xabi,
I am also interested in OpenFOAM deals with wall functions. In which file did you find the
equation epsilon_[faceCelli] +=Cmu75*pow(k_[faceCelli], 1.5)/(kappa_.value()*RASModel::y_[patchi][facei]); you mention in 2.? Thanks a lot!

 MaLa February 25, 2014 12:24

Hi

On this note of the epsilonWallFunction, does anybody know the source of the formulation mentioned above by Sven? I wish to know the reasoning behind why epsilon @ the first node near wall is recalculated this way.

If anyone can direct me to the scientific article, which forms the basis of the epsilonWallFunction, I would be grateful. Thanks.

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