[ehsan]

Dear All

I need a reference that OpenFOAM used to write the following formula for nutWallFunction:

scalar yPlus = Cmu25*y[faceI]*sqrt(k[faceCellI])/nuw[faceI];

if (yPlus > yPlusLam_)
{
nutw[faceI] = nuw[faceI]*(yPlus*kappa_/log(E_*yPlus) - 1.0);
}
}

I am asked about "Near Wall Treatment" formula in K-W SST in OpenFOAM,
In fact, I need near wall treatment for all parameters including
U, k and <omega>

I read the paper mentioned here (
Progress in ...).
I could not find source codes for other parameters U and K and Omega in OpenFOAM. Only nuT is available.

Regards
Ehsan

[ehsan]

Hello,

1- I am asked about:

The formula used to determine the near wall values of U, k and <omega> in K-W SST model in OpenFOAM. May I ask you whether OpenFOAM uses exactly the same formula given in:

http://www.zaidan.info/seikabutsu/20...okyo_ts059.pdf

If no, which reference is used for OpenFOAM formulations?

2- In nutkWallFunction.C, it is:
nut = nu * ((y+ * k) / ln( E * y+) - 1)

which means: nut=nu[(y+/U+)-1]

May I ask you the refernce of this equation?

Regards

[RodriguezFatz]

ehsan,
The omega b.c. of the paper is implemented in openfoam, see:
https://github.com/OpenFOAM/OpenFOAM...hScalarField.C
line 223 to 235.
They (in the paper) use a zero-flux boundary condition for k, so this would be zeroGradient boundary condition in openFoam.
The nut damping is not implemented in openFoam, that's why people use one of the other nut b.c., such as the one you wrote.
If you want the low-Re version as in the paper, I implemented it:
http://www.cfd-online.com/Forums/openfoam-programming-development/134102-komegasst-lowre-damping-fluent.html#post491414
(I didn't compare everything, but I guess it is the same as in the paper).


Do you want to use a low-Re or a high-Re version?

[ehsan]

Thank you very much. Your helps are very fruitful for me.

I already used K-W SST and LES in OpenFOAM and was asked by the reviewer of my paper about near wall treatments:

1- OK, w is like the paper, K is zero gradient, and nut from the formula I mentioned, how the latter transforms to the velocity? and does it has a reference?

2- In LES, I used "kqRWallFunction" for k, and nothing for other parameters (like a test case in hand. May I ask you about the near wall treatments in LES?

3- And I also have a question about LES delta that I used, that is smooth. I also need its relation with the cell size (or a reference)

Regards
Ehsan

[RodriguezFatz]

1) You mean if the wall shear is used as b.c. for the velocity in the first cell? I don't know that.
Unfortunately, I can not help with the other question, too. Sorry.

[ehsan]

No, I mean where does this nut show itself in calculations? Is it in shear stress calculation in the domain. I mean as OF does not use Eq. 17 of that paper, how it compensate?

[RodriguezFatz]

You can find nut evaluation in the komegasst turbulence model, directly after solving of k and omega differential equation.

[ehsan]

OK, Thanks. The only problem is U, that is not used in OpenFOAM. It is written in the paper below Eq 18:

"This formulation gives the relation between the velocity near the wall and the wall shear stress."

So, if we correct wall shear stress with that nut, maybe we could find u correctly as well.

[ehsan]

Hi

I need to know near wall treatments in LES. In LES, I used "kqRWallFunction" for k, and nothing for other parameters (like a test case in hand). May I ask you about the near wall treatments in LES?

2- And I also have a question about LES delta that I used, that is smooth. I also need its relation with the cell size (or a reference)

Regards

[ehsan]

I had an inquiry on the near wall treatment in LES.

OpenFOAM mainly follows Florian MENTER algorithm for wall treatment in K-W SST (http://www.zaidan.info/seikabutsu/20...okyo_ts059.pdf). However, OpenFOAM uses the same near wall treatment for LES as K-W SST (kqRwallfunction for K and nothing for others). May I ask you whether it is a correct and standard way in near wall treatments in LES?

[ehsan]

LES deltas

smoothDelta Smoothing of delta

I am asked about the:

the formula used for the LES filter width as a function of grid size for smoothDelta. Would you please help?

[hfs]

Hi,

I also would like to know:
when "kqRwallfunction" is used in k boundary conditions (when LES is used), will that even matter? Will OpenFOAM apply it or it is totally ignored (cuz it corresponds to RANS and not to LES)?
If using "kqRwallfunction" in LES is wrong, what will OpenFOAM apply instead: zeroGradient or fixedValue = 0?

[RodriguezFatz]

Originally Posted by ehsan

However, OpenFOAM uses the same near wall treatment for LES as K-W SST...

Ehsan, I don't think this is a correct description of how this works. OpenFOAM offers serveral boundary conditions and you can use the one you want to in each case and at each single boundary. It's not OpenFOAM that does this but the user.

Also, thinking of a RANS model and an LES using the same wall function is not correct. RANS models use wall functions that model time-averaged values as a function of other time-averaged values. LES wall functions model instantaneous values that are spatially filtered. This is quite different. Even though functions might look the same they have a different physical meaning.

[ehsan]

Hello,


Please see Sec. 4.2.2 in http://www.cimec.org.ar/ojs/index.ph...File/3263/3186

(Thanks to Dr Santiago Márquez Damián for his kind helps)

[Jasper Z]

Originally Posted by ehsan

LES deltas

smoothDelta Smoothing of delta

I am asked about the:

the formula used for the LES filter width as a function of grid size for smoothDelta. Would you please help?

Hi Ehsan,

Sorry to start this thread again. I am facing the same problem, have you figured out the formula for the smooth filter width in OpenFOAM? Is there any tutorial about this? Many thanks