Getting the WallFunctionCoeffs

markh83 · October 1, 2008, 05:49

Hi..

I'm trying to simulate a flow over an inclined step using TurbFoam and k-epsilon..

I would like to add a surface roughness to bottom face.. For this I've found the wallFunctionCoeffs, kappa and E.. Kappa is of course von Karman's constant (0.4187), but what is E? From Computational Fluid Dynamics (2007) by Versteeg & Malalasekera I can derive, that it is an integration constant that depends on the wall roughness and that E for a smooth wall is 9.793, and the book just ends by saying that E should be varied for other surfaces.. It then refers to Boundary Layer Theory (1979) by Schlichting. I've got my hand on the 2000 edition of this book, but in this, they use another formula.

The one I believe OpenFOAM uses is :
uPlus = (1/kappa)*ln(E*yPlys)

and the one from Sclichting is:
uPlus = (1/kappa)*ln(yPlus)+CPlus

So I still have the problem of not really knowing the correlation between surface roughness height and E.. Can anyone here name a book or give me a link to a source, concerning E, or just some values for E at different rougness'es?

lin · October 1, 2008, 06:58

Just one point.The two equations are basically the same.

1./0.4187*log(9.793)= 5.4494,which should be the CPlus value .

In fact,the CPlus value I remember is 5.5

markh83 · October 1, 2008, 12:01

Thank you for the quick answer..

Yes, I know that the one can be isolated from the other. The problem is, that CPlus also seems to be emperical and i also need info on that one..

I have now ordered the 1979 edition of the Schlichting book, since my Versteeg book specifically says, that there ought to be tables for E in this..

October 1, 2008, 05:49	Hi.. I'm trying to simulate	#1
markh83 New Member Mark Herskind Join Date: Mar 2009 Posts: 8 Rep Power: 17	Hi.. I'm trying to simulate a flow over an inclined step using TurbFoam and k-epsilon.. I would like to add a surface roughness to bottom face.. For this I've found the wallFunctionCoeffs, kappa and E.. Kappa is of course von Karman's constant (0.4187), but what is E? From Computational Fluid Dynamics (2007) by Versteeg & Malalasekera I can derive, that it is an integration constant that depends on the wall roughness and that E for a smooth wall is 9.793, and the book just ends by saying that E should be varied for other surfaces.. It then refers to Boundary Layer Theory (1979) by Schlichting. I've got my hand on the 2000 edition of this book, but in this, they use another formula. The one I believe OpenFOAM uses is : uPlus = (1/kappa)ln(EyPlys) and the one from Sclichting is: uPlus = (1/kappa)*ln(yPlus)+CPlus So I still have the problem of not really knowing the correlation between surface roughness height and E.. Can anyone here name a book or give me a link to a source, concerning E, or just some values for E at different rougness'es?

October 1, 2008, 06:58	Just one point.The two equatio	#2
lin Senior Member Hua Zen Join Date: Mar 2009 Posts: 138 Rep Power: 17	Just one point.The two equations are basically the same. 1./0.4187*log(9.793)= 5.4494,which should be the CPlus value . In fact,the CPlus value I remember is 5.5

October 1, 2008, 12:01	Thank you for the quick answer	#3
markh83 New Member Mark Herskind Join Date: Mar 2009 Posts: 8 Rep Power: 17	Thank you for the quick answer.. Yes, I know that the one can be isolated from the other. The problem is, that CPlus also seems to be emperical and i also need info on that one.. I have now ordered the 1979 edition of the Schlichting book, since my Versteeg book specifically says, that there ought to be tables for E in this..