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-   -   yPlus query (http://www.cfd-online.com/Forums/openfoam/69590-yplus-query.html)

vw.cfd October 28, 2009 06:02

yPlus query
 
Hi,

I have a basic query regarding the yPlus value and the associated(or appropriate) turbulence model, I wish to use the k-omega+SST model. What should be the appropriate yPlus value for good functioning of this model on openFoam. I have read in several threads that for K-epsilon model the yPlus should be in the log layer (y+>10). Is it the same case with komega+SST or should it be in the laminar sub-layer?

thnX!!

Simon Lapointe October 28, 2009 08:06

The kOmegaSST model in OpenFOAM uses wall functions and thus requires a high y+ value. However, in 1.5-dev there is a kOmegaSST_LowRe which, I think, can resolve the near-wall region and should be used with a small y+.

Hope this helps

vw.cfd October 28, 2009 10:20

Hi Simon,

I will try this out.

ThanX!!

vw.cfd October 29, 2009 08:53

Hi Simon,

I tried your suggestion on openfoam 1.5-dev,

I obtain this error message:

Unknown RASModel type kOmegaSST_LowRe
Valid RASModel types are :
15
(
NonlinearKEShih
kEpsilon
realizableKE
LienCubicKELowRe
LienLeschzinerLowRe
LaunderSharmaKE
laminar
SpalartAllmaras
LienCubicKE
LamBremhorstKE
RNGkEpsilon
LRR
QZeta
LaunderGibsonRSTM
kOmegaSST
)

Which turbulence model did you mean exactly?

ThnX!!

Simon Lapointe October 29, 2009 10:24

Hi varun,

The kOmegaSST_LowRe model has been added recently to OpenFOAM-1.5-dev so you need to update your OpenFOAM (or download the model source code) to get it.

idrama February 18, 2010 10:08

Hey, foamers!

I am already using OpenFOAM 1.6. The mentioned mole does not exist.

Cheers

MadsR February 22, 2010 06:44

bump - any new info on this?

wenterodt February 23, 2010 04:25

The source of the kOmegaSST_lowRe model can be downloaded here:
http://openfoam-extend.svn.sourcefor.../?pathrev=1415
it does not directly compile with 1.6, though only little changes neccessary:

at kOmegaSST_LowRe/kOmegaSST_LowRe.C line 171 add
Code:

kappa_
    (
        dimensioned<scalar>::lookupOrAddToDict
      (
          "kappa",
            coeffDict_,
          0.41
      )
    ),

and at line 313 add
Code:

kappa_.readIfPresent(coeffDict_);
in kOmegaSST_LowRe/kOmegaSST_LowRe.H add at line 131
Code:

dimensionedScalar kappa_;
I have used it in 1.6 a lot so far in 1d and 2d problems obtaining very good results (pipes, channels, plate heat exchangers, tube bundle heat exchangers).
BUT I face major problems in 3d geometries, where the model results in distinct pressure fronts in the domain, which then make the calculation crash.

I'd be glad for any ideas on that!

//Tammo

idrama February 23, 2010 07:15

Hello wenterodt,

could you please post the procedure to install it in OpenFOAM-1.6?

Cheers,

Claus

wenterodt February 23, 2010 08:19

Basically just write Make/files and Make/options, compile (wmake libso) and add a line to the controlDict

The procedure is pretty much the same as described here:
http://www.tfd.chalmers.se/~hani/kurser/OS_CFD_2008/implementTurbulenceModel.pdf

// Tammo

Pekka March 3, 2010 16:12

Wall function on LowRe model
 
Hello Tammo,


have you any experience in nut boundary conditions on kOmegaSST_LowRe RAS model. It is zeroGradient or some nut wall function?


Thanks.

idrama March 10, 2010 15:39

Hey Foamers!

I do not understand the purpose of yPlus. I found that tool yPlusRAS and executed. I got this values, but what should I do with these? I have been watching in many books.

Cheers,

Claus


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