wall functions.-E value, epsilon calculation

Xabi · April 5, 2009, 05:40

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.

Thank you in advance,
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!

April 5, 2009, 05:40	wall functions.-E value, epsilon calculation	#1
Xabi New Member Join Date: Mar 2009 Posts: 20 Rep Power: 6	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] +=Cmu75pow(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. Thank you in advance, Xabi

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September 10, 2009, 13:57		#2
svens Member Sven Schweikert Join Date: Jun 2009 Posts: 38 Rep Power: 6	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

September 11, 2009, 18:54		#3
sven Member Sven Winkler Join Date: May 2009 Posts: 70 Rep Power: 6	Hey Xabi, I am also interested in OpenFOAM deals with wall functions. In which file did you find the equation epsilon_[faceCelli] +=Cmu75pow(k_[faceCelli], 1.5)/(kappa_.value()RASModel::y_[patchi][facei]); you mention in 2.? Thanks a lot!