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-   -   Conditions in which yPlus does not matter (https://www.cfd-online.com/Forums/openfoam-solving/152120-conditions-yplus-does-not-matter.html)

Yuby April 24, 2015 05:07
Conditions in which yPlus does not matter
 
Hi FOAMers!

I am running a turbulence case of an incompressible flow around a rotating disc. The yPlusRAS utility gives me this values:

Code:
Patch 5 named cuerpo y+ : min: 0.0062716 max: 42.1937 average: 3.33432

Patch 6 named bordes y+ : min: 0.0042175 max: 15.3098 average: 2.02145
It's very difficult to get the yPlus you want, as it is a rotating geometry the wall shear stresses vary too much. I have spent months with snappyhexmesh...

My question is: Does a combination of turbulence model+boundary conditions at the walls/wall function exist in which the yPlus value doesn't matter?

As I have read, omegaWallfunction can change from Low-Re to High-Re, but in this thread is not completely clear: http://www.cfd-online.com/Forums/ope...omega-sst.html The paper of Menter agrees.

So, I am a little bit worried, because I don't know what to do. In this paper http://www.tfd.chalmers.se/~hani/kur...DES-Report.pdf, the only wall function they use is the omegaWallfunction, and they don't talk about yPlus, so I don't know if it does matter....

Can you help me? I would like to finish my thesis, but I am confused.. :confused:

Thank you very much in advance :) !!!

Yuby April 24, 2015 05:19
My current boundary conditions are:

kinetic energy:
Code:
  GNU nano 2.2.6                      Archivo: 0.org/k                                                   

/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  2.3.0                                |
|  \\  /    A nd          | Web:      www.OpenFOAM.org                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version    2.0;
    format      ascii;
    class      volScalarField;
    object      k;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

#include        "include/initialConditions"

dimensions      [0 2 -2 0 0 0 0];

internalField  uniform $turbulentKE;

boundaryField
{
    inlet
    {
        type            fixedValue;
        value          uniform $turbulentKE;
    }
    outlet
    {
        type            zeroGradient;
    }

    cuerpo
    {
        type            kqRWallFunction;
        value          $turbulentKE;
    }
    bordes
    {
        type            kqRWallFunction;
        value          $turbulentKE;
    }

    #include "include/frontBackUpperPatches"
}


// ************************************************************************* //
Omega:

Code:

  GNU nano 2.2.6                      Archivo: omega                                                     

/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  2.3.1                                |
|  \\  /    A nd          | Web:      www.OpenFOAM.org                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version    2.0;
    format      ascii;
    class      volScalarField;
    location    "0";
    object      omega;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

#include        "include/initialConditions"

dimensions      [0 0 -1 0 0 0 0];

internalField  uniform $turbulentOmega;

boundaryField
{
    inlet
    {
        type            fixedValue;
        value          uniform $turbulentOmega;
    }
    outlet
    {
        type            zeroGradient;
    }
    cuerpo
    {
        type            omegaWallFunction;
        value          uniform $turbulentOmega;
    }
    bordes
    {
        type            omegaWallFunction;
        value          uniform $turbulentOmega;
    }
    #include "include/frontBackUpperPatches"
}


// ************************************************************************* //
nuT:

Code:
  GNU nano 2.2.6                      Archivo: nut                                                     

/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  2.3.0                                |
|  \\  /    A nd          | Web:      www.OpenFOAM.org                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version    2.0;
    format      ascii;
    class      volScalarField;
    location    "0";
    object      nut;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 2 -1 0 0 0 0];

internalField  uniform 0;

boundaryField
{
    inlet
    {
        type            calculated;
        value          uniform 0;
    }

    outlet
    {
        type            calculated;
        value          uniform 0;
    }

    cuerpo
    {
        type            nutkWallFunction;
        value          uniform 0;
    }
    bordes
    {
        type            nutkWallFunction;
        value          uniform 0;
    }
#include "include/frontBackUpperPatches"
}


// ************************************************************************* //

frontBackUpperPatches:

Code:
  GNU nano 2.2.6                Archivo: frontBackUpperPatches                                         

/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  2.3.0                                |
|  \\  /    A nd          | Web:      www.OpenFOAM.org                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/

top
{
    type slip;
}

bottom
{
    type slip;
}

frontandback
{
    type slip;
}

// ************************************************************************* //

initialconditions:

Code:
  GNU nano 2.2.6                  Archivo: initialConditions                                             

/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  2.3.0                                |
|  \\  /    A nd          | Web:      www.OpenFOAM.org                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
//Para un Re= 270000
flowVelocity        (15 0 0);

//6 revoluciones por segundo, de Flight Dynamics Measurements on an Instrumented Frisbee
//Ralph D Lorenz
//Lunar and Planetary Laboratory,
//University of Arizona
omegadisk            37.7;

pressure            0;

//turbulentKE=(3/2)*(UI)²
//Para U=15; I=0.005;
//turbulentKE=k=0.02434614
turbulentKE          0.0084375;

//http://www.cfd-online.com/Tools/turbulence.php
//http://www.esi-cfd.com/faq/index.php?action=artikel&cat=4&id=156&artlang=en
turbulentOmega      1125;

#inputMode          merge

// ************************************************************************* //
for a Standard k-omega model

romant April 24, 2015 07:23
Quote:
Originally Posted by Yuby (Post 543527)
Hi FOAMers!

I am running a turbulence case of an incompressible flow around a rotating disc. The yPlusRAS utility gives me this values:

Code:
Patch 5 named cuerpo y+ : min: 0.0062716 max: 42.1937 average: 3.33432

Patch 6 named bordes y+ : min: 0.0042175 max: 15.3098 average: 2.02145
It's very difficult to get the yPlus you want, as it is a rotating geometry the wall shear stresses vary too much. I have spent months with snappyhexmesh...

My question is: Does a combination of turbulence model+boundary conditions at the walls/wall function exist in which the yPlus value doesn't matter?

As I have read, omegaWallfunction can change from Low-Re to High-Re, but in this thread is not completely clear: http://www.cfd-online.com/Forums/ope...omega-sst.html The paper of Menter agrees.

So, I am a little bit worried, because I don't know what to do. In this paper http://www.tfd.chalmers.se/~hani/kur...DES-Report.pdf, the only wall function they use is the omegaWallfunction, and they don't talk about yPlus, so I don't know if it does matter....

Can you help me? I would like to finish my thesis, but I am confused.. :confused:

Thank you very much in advance :) !!!

There are no RANS turbulence models which depend on y+ on one way other another. However, you could try to use the approach described in post 3 of the thread that you mentioned http://www.cfd-online.com/Forums/ope...tml#post306339 with the nutUSpaldingWallFunction for nut.


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