Originally Posted by niklas (Post 196228)

I have added surface roughness according to the fluent manual.
found for instance here http://web.njit.edu/topics/Prog_Lang_Docs/html/FLUENT/fluent/fluent5/ug/html/nod e195.htm

What I did was to add

Ks_
(
dimensioned<scalar>::lookupOrAddToDict
(
"Ks",
subDict("wallFunctionCoeffs"),
0.0
)
),

Cs_
(
dimensioned<scalar>::lookupOrAddToDict
(
"Cs",
subDict("wallFunctionCoeffs"),
0.0
)
),

to RASModel.H and the corresponding stuff in RASModel.C

and in wallViscosityI.H i modified the for-loop to

forAll(curPatch, facei)
{
label faceCelli = curPatch.faceCells()[facei];

scalar uStar = Cmu25*sqrt(k_[faceCelli]);
scalar yPlus = y_[patchi][facei]*uStar/nuw[facei];
scalar KsPlus = Ks_.value()*uStar/nuw[facei];

// hydrodynamically smooth
scalar logDB = 1.0;

if (KsPlus > 2.25)
{
// fully rough
if (KsPlus > 90.0)
{
logDB = 1.0 + Cs_.value()*KsPlus;
}
else
// transitional
{
scalar n = ::sin(0.4258*(log(KsPlus) - 0.811))
scalar a = (KsPlus - 2.25)/87.75 + Cs_.value()*KsPlus;
logDB = ::pow(a, n);
}
}

if (yPlus > yPlusLam_)
{
nutw[facei] =
nuw[facei]
*(yPlus*kappa_.value()/log(E_.value()*yPlus/logDB) - 1);
}
else
{
nutw[facei] = 0.0;
}
}

using the facts that
log(A)-log(B) = log(A/B)
log(A)*n = log(A^n)

you essentially just need to divide the wall constant E with the variable logDB.

Normally setting the constants to zero would revert to the normal smooth approach, but not here and that is easily fixed also.
But is there anything else I need to modify that I have missed or is this all I have to do?

N