CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Post-Processing

yplus postProcessing formula

Register Blogs Community New Posts Updated Threads Search

Like Tree1Likes
  • 1 Post By immortality

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 26, 2013, 08:16
Default yplus postProcessing formula
  #1
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,208
Rep Power: 26
immortality is on a distinguished road
where does this formula that is used for yPlus come from?!
I have not seen such expression so far but differently.where can I find an article or page about such expression?
Code:
turbulence {
        type executeIfObjectExists;
        objectName k;
        checkType true;
        //        checkType false;
        objectType volScalarField;
        objectShouldExist true;
        //        writeDebug true;
        readDuringConstruction false;

        functions {
            yPlusField
            {
                type expressionField;
                outputControl timeStep;
                outputInterval 1;
                fieldName yPlus;
                expression "pow(0.09,0.25)*sqr(k)*nearDist()/mu";
                autowrite true;
            }
            yPlusWall
            {
                type patchExpression;
                expression "pow(0.09,0.25)*sqr(k)*dist()/mu";
                accumulations (
                    min
                    max
                    average
                );
                patches (wall);
                verbose true;
            }
        }
    }
__________________
Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King.
To Be or Not To Be,Thats the Question!
The Only Stupid Question Is the One that Goes Unasked.
immortality is offline   Reply With Quote

Old   April 26, 2013, 22:18
Default
  #2
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,208
Rep Power: 26
immortality is on a distinguished road
i have found that this expression is y star not y plus.
How such an obvious mistake has been made here in a tutorial of OpenFOAM?
__________________
Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King.
To Be or Not To Be,Thats the Question!
The Only Stupid Question Is the One that Goes Unasked.
immortality is offline   Reply With Quote

Old   May 2, 2013, 14:18
Default
  #3
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,208
Rep Power: 26
immortality is on a distinguished road
how can modify it to true expression?very important to me.
(my case is compressible,kOmegaSST turbulence model)
__________________
Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King.
To Be or Not To Be,Thats the Question!
The Only Stupid Question Is the One that Goes Unasked.
immortality is offline   Reply With Quote

Old   May 5, 2013, 08:34
Default
  #4
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,208
Rep Power: 26
immortality is on a distinguished road
in mutkWallFunctionFvPatchScalarField the equation uses for y-plus is related to y-star not y-plus

Code:
y-star=pow(0.09,0.25)*sqr(k)*nearDist()/mu
Code:
y-plus=rho*u_star*y/mu which u*=aqrt(taw_w/rho)
y-star is related to turbulent kinetic energy while y-plus relates to friction velocity(that relates to wall skin friction in its own)

in the code of mut
:
Code:
forAll(mutw, faceI)
    {
        label faceCellI = patch().faceCells()[faceI];

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

        if (yPlus > yPlusLam_)
        {
            mutw[faceI] = muw[faceI]*(yPlus*kappa_/log(E_*yPlus) - 1);
        }
    }
thanks.
__________________
Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King.
To Be or Not To Be,Thats the Question!
The Only Stupid Question Is the One that Goes Unasked.
immortality is offline   Reply With Quote

Old   May 5, 2013, 11:16
Default
  #5
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,208
Rep Power: 26
immortality is on a distinguished road
I reported this as a bug:
http://www.openfoam.org/mantisbt/view.php?id=835
could anyone help.the answer is not acceptable to me.I want to know the true yPlus in a turbulent kOmegaSST with yplus<=1 to be sure that separation regions and adverse pressure gradients are calculated and included truely not through some "wall-function rough estimations".
maybe someone dosn't want to use wall functions.
I want "y plus" exactly and only "y plus" not "y star" or any other thing instead of "y plus"
could anyone help?
please don't hesitate.
(I have see some modified files for yPlusRAS but they don't work in 2.2.0 version)
lpz456 likes this.
__________________
Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King.
To Be or Not To Be,Thats the Question!
The Only Stupid Question Is the One that Goes Unasked.
immortality is offline   Reply With Quote

Reply


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
[Other] Contribution a new utility: refine wall layer mesh based on yPlus field lakeat OpenFOAM Community Contributions 58 December 23, 2021 02:36
How to calculate Y+( Yplus) mohammad Main CFD Forum 3 January 11, 2011 23:23
which yplus (SST) sanchezz CFX 17 January 11, 2010 04:45
Benetton Formula 1 CD adapco Group Marketing Siemens 13 February 7, 2002 09:33
heat transfer coefficients with "bad" yplus Andrew Main CFD Forum 4 April 8, 1999 04:43


All times are GMT -4. The time now is 19:35.