[shock77]

Hi,


Usually I always had noSlip walls when running numerical simulations. Now, I have a case where I need to apply slip boundary conditions. I wonder what boundary condition I should use for k, omega and alphat when using the k-omega-SST model. Do I use zeroGradient or slip for those?


Kind regards,
Shock77

[saeed jamshidi]

Quick answer:

I think the below condition is the answer, but I'm not sure:

	
    wall
    {   
        type            slip;
    }

this is true for K & omega.

[shock77]

Thank you for your reply and input!


I couldnt find anyone who uses slip in combination with turbulence models. It feels also kind of weird to be honest and counter intuitive. Have you ever used this combination?

[saeed jamshidi]

Yes, I have.

When I want to simulate flow over cylinder (3D) I consider slip BC for the top & Bottom as well as for the front & Back with K-omega SST.

Besides, you can have a look at the motorbike tutorial in simpleFoam, just focus on BCs.

\\wsl.localhost\Ubuntu18.04\home\saeedfoam\OpenFOAM\tutorials\incompressible\simpleFoam\motorBike

Good luck.

[shock77]

Good to know, thank you!


In the tutorial they use wall functions. Do you mean another tutorial by any chance?

[saeed jamshidi]

I have read some materials and found that utilization of wall functions is a merit, because you set yplus abouve 30 and it reduces computational time cost. However, I'm looking for the tutorials without treating walls with wall functions to understand the boundary conditions of walls for k, omega and nut.

[shock77]

So is there any tutorial that uses slip for k, omega or epsilon?

[Yann]

Originally Posted by shock77

So is there any tutorial that uses slip for k, omega or epsilon?

You can check the tutorials, for instance:

grep -r "slip" $FOAM_TUTORIALS | grep "/omega"

Cheers,
Yann

[saeed jamshidi]

As you can see from motorbike tutorial, upperWall was considered as slip:

upperWall
{
    type slip;
}

frontAndBack
{
    type slip;
}

for example, have a look at part of k :

    lowerWall
    {
        type            kqRWallFunction;
        value           $internalField;
    }

    motorBikeGroup
    {
        type            kqRWallFunction;
        value           $internalField;
    }

    #include "include/frontBackUpperPatches"

wall functions are used when we have noslip BC (such as on motorbike or lower wall), while in slip condition (upper wall) we assign slip for k (assigned by include command), omega or epsilon.

upper wall actually is not a real wall and in real world does not exist. we just consider it in our simulation.

So, you should consider this in all k, omega or epsilon dictionaries in zero folder:

Wall
{
type slip;
}

[saeed jamshidi]

Originally Posted by Yann

You can check the tutorials, for instance:

grep -r "slip" $FOAM_TUTORIALS | grep "/omega"

Cheers,
Yann

Hi Yann,

Have you ever seen a tutorial without using wall functions on walls? specially for k-omega sst model.

Thanks

[shock77]

Originally Posted by Yann

You can check the tutorials, for instance:

grep -r "slip" $FOAM_TUTORIALS | grep "/omega"

Cheers,
Yann

Thank you very much! Seems like there is no usage of slip for omega or k in the tutorials.

[shock77]

Originally Posted by saeed jamshidi

As you can see from motorbike tutorial, upperWall was considered as slip:

upperWall
{
    type slip;
}

frontAndBack
{
    type slip;
}

for example, have a look at part of k :

    lowerWall
    {
        type            kqRWallFunction;
        value           $internalField;
    }

    motorBikeGroup
    {
        type            kqRWallFunction;
        value           $internalField;
    }

    #include "include/frontBackUpperPatches"

wall functions are used when we have noslip BC (such as on motorbike or lower wall), while in slip condition (upper wall) we assign slip for k (assigned by include command), omega or epsilon.

upper wall actually is not a real wall and in real world does not exist. we just consider it in our simulation.

So, you should consider this in all k, omega or epsilon dictionaries in zero folder:

Wall
{
type slip;
}

I cannot see a slip assigned to k in the tutorials or in the code you copied. Interestingly, my tutorial is different from yours (I am using Openfoam 5). For U I get:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  5                                     |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volVectorField;
    location    "0";
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

#include        "include/initialConditions"

dimensions      [0 1 -1 0 0 0 0];

internalField   uniform $flowVelocity;

boundaryField
{
    //- Set patchGroups for constraint patches
    #includeEtc "caseDicts/setConstraintTypes"

    #include "include/fixedInlet"

    outlet
    {
        type            inletOutlet;
        inletValue      uniform (0 0 0);
        value           $internalField;
    }

    lowerWall
    {
        type            fixedValue;
        value           $internalField;
    }

    motorBikeGroup
    {
        type            noSlip;
    }

    #include "include/frontBackUpperPatches"
}


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

For k:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  5                                     |
|   \\  /    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
{
    //- Set patchGroups for constraint patches
    #includeEtc "caseDicts/setConstraintTypes"

    //- Define inlet conditions
    #include "include/fixedInlet"

    outlet
    {
        type            inletOutlet;
        inletValue      $internalField;
        value           $internalField;
    }

    lowerWall
    {
        type            kqRWallFunction;
        value           $internalField;
    }

    motorBikeGroup
    {
        type            kqRWallFunction;
        value           $internalField;
    }

    #include "include/frontBackUpperPatches"
}


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

[saeed jamshidi]

Please have a look at your 0/ include folder.

You will see some BCs there.

Allways they are included to your K or U .... by #include "include/frontBackUpperPatches".

I am using OpenFoam v2112.

[shock77]

Ohhh now I see it, thank your very much again!