[fidu]

Hi foamer

I need to achieve a cell aspect ratio 1:1:1 at the snappy region of my background mesh to the geometry at my ground. A I am able to adopt a previous code which already achieved this but I had to split the domain into two boxes, a near ground region and a ceiling region. My question now is, how can I achieve this in the best way? I am quite new to the entire CFD universe and so I am a bit confused. My approach would have been just to take the same multi-graded mesh in both boxes an keep the same amount of cells. As my near ground region is much smaller this would have the desired effect of having the finer mesh in this region. However I am firstly not quite sure if this fulfill the requirement of the desired cell aspect ratio and secondly I think this would not be a efficient solution....

So my blockMeshDict is right now this:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.4.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

backgroundMesh
{
    xMin   1.9; // L = 
    xMax   8.3;
    yMin   0.0054; // L = 
    yMax   1.9;
    zMin     0;   //-0.01875
    zTree   0.0.09375;      //15m/160
    zMax   1.61675;   //1.6
    xCells  141;    //141   800
    yCells  62;     //62  200
    zCells  32;    //32   200



}

//convertToMeters 1;

vertices
(
    ($:backgroundMesh.xMin $:backgroundMesh.yMin $:backgroundMesh.zMin)  //0
    ($:backgroundMesh.xMax $:backgroundMesh.yMin $:backgroundMesh.zMin) //1
    ($:backgroundMesh.xMax $:backgroundMesh.yMax $:backgroundMesh.zMin) //2
    ($:backgroundMesh.xMin $:backgroundMesh.yMax $:backgroundMesh.zMin) //3

    ($:backgroundMesh.xMin $:backgroundMesh.yMin $:backgroundMesh.zMax) //4
    ($:backgroundMesh.xMax $:backgroundMesh.yMin $:backgroundMesh.zMax) //5
    ($:backgroundMesh.xMax $:backgroundMesh.yMax $:backgroundMesh.zMax) //6
    ($:backgroundMesh.xMin $:backgroundMesh.yMax $:backgroundMesh.zMax) //7

    ($:backgroundMesh.xMin $:backgroundMesh.yMin $:backgroundMesh.zTree)    //8    new 4 
    ($:backgroundMesh.xMax $:backgroundMesh.yMin $:backgroundMesh.zTree)    //9     new 5
    ($:backgroundMesh.xMax $:backgroundMesh.yMax $:backgroundMesh.zTree)    //10    new 6
    ($:backgroundMesh.xMin $:backgroundMesh.yMax $:backgroundMesh.zTree)    //11    new 7

);

blocks
(
    hex (0 1 2 3 8 9 10 11)               //0 1 2 3 4 5 6 7   domain of ground to zTree
    (
        $:backgroundMesh.xCells
        $:backgroundMesh.yCells
        $:backgroundMesh.zCells
    ) 

    simpleGrading 
    (  
        ( 
            (0.109375 0.085106383 0.3)    // l% x-dir, % cells, expansion =  
            (0.53125  0.780141844 1)    // l% x-dir, % cells, expansion =  
            (0.359375 0.134751773 10) // l% x-dir, % cells, expansion =  
        ) 
        1                  // y-direction expansion ratio
        (                  
            (0.1572376 0.375 1)    // z% x-dir, % cells, expansion =      
            (0.8427624 0.625 8)    // z% x-dir, % cells, expansion =               
        )  
    ) 

    hex (8 9 10 11 4 5 6 7)               //0 1 2 3 4 5 6 7 domain of zTree to ceilling   hex (8 9 10 11 4 5 6 7)
    (
        $:backgroundMesh.xCells
        $:backgroundMesh.yCells
        $:backgroundMesh.zCells
    )


    simpleGrading 
    (  
        ( 
            (0.109375 0.085106383 0.3)    // l% x-dir, % cells, expansion =  
            (0.53125  0.780141844 1)    // l% x-dir, % cells, expansion =  
            (0.359375 0.134751773 10) // l% x-dir, % cells, expansion =  
        ) 
        1                  // y-direction expansion ratio
        (                  
            (0.1572376 0.375 1)    // z% x-dir, % cells, expansion =      
            (0.8427624 0.625 8)    // z% x-dir, % cells, expansion =               
        )  
    ) 

);

edges
(
);

boundary
(
    inlet
    {
        type patch;
        faces
        (
            (0 3 11 8)
            (8 11 7 4)       //(0 3 7 4)
        );
    }

    outlet
    {
        type patch;
        faces
        (
            (1 9 10 2)
            (9 5 6 10)       //(1 5 6 2)
        );
    }

    ground
    {
        type wall;
        faces
        (
            (0 1 2 3)       //(0 1 2 3)
        );
    }

    frontAndBack
    {
        type wall;
        faces
        (
            (0 8 9 1) (8 4 5 9)                 //front (0 4 5 1) 
            (3 2 10 11) (11 10 6 7)             //back (3 2 6 7)
            (4 7 6 5)                           //ceilling (4 7 6 5)
        );
    }

);



mergePatchPairs
(
);

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

and my snappyhexmeshDict is:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.4.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      snappyHexMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

#includeEtc "caseDicts/mesh/generation/snappyHexMeshDict.cfg"

castellatedMesh on;
snap            on;
addLayers       off;

geometry
{
    GltbuildingclusterWindtunnel.stl
    {
        scale 0.001;
        type triSurfaceMesh;
        name GltbuildingclusterWindtunnel;
    }

};

castellatedMeshControls
{
//    nCellsBetweenLevels 3;

    features
    (
      { file  "GltbuildingclusterWindtunnel.eMesh"; level 3; scale 0.001;}
    );

    refinementSurfaces
    {
        GltbuildingclusterWindtunnel
        {
            level (2 3);
            patchInfo { type wall; }
        }
    }

    refinementRegions
    {
        GltbuildingclusterWindtunnel
        {
            mode distance;
            levels ((0.077 2)); 
        }
    }

    locationInMesh (2 1 1);

    resolveFeatureAngle 60;
    allowFreeStandingZoneFaces true;

}

snapControls
{
    //- Number of patch smoothing iterations before finding correspondence
    //  to surface
    nSmoothPatch 3;

    //- Relative distance for points to be attracted by surface feature point
    //  or edge. True distance is this factor times local
    //  maximum edge length.
    tolerance 2.0;

    //- Number of mesh displacement relaxation iterations.
    nSolveIter 30;

    //- Maximum number of snapping relaxation iterations. Should stop
    //  before upon reaching a correct mesh.
    nRelaxIter 5;


    // Feature snapping

        //- Number of feature edge snapping iterations.
        //  Leave out altogether to disable.
        nFeatureSnapIter 10;

        //- Detect (geometric) features by sampling the surface (default=false)
        implicitFeatureSnap true;

        //- Use castellatedMeshControls::features (default = true)
        explicitFeatureSnap false;
}

addLayersControls
{
    layers
    {
        "CAD.*"
        {
            nSurfaceLayers 2;
        }
    }

    relativeSizes       true;
    expansionRatio      1.2;
    finalLayerThickness 0.5;
    minThickness        1e-3;
}

meshQualityControls
{

maxConcave 70;
minTetQuality 1E-12;
maxInternalSkewness 5;
maxBoundarySkewness 25;
}

writeFlags
(
    scalarLevels
    layerSets
    layerFields
);

mergeTolerance 1e-6;

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

I hope this is not a too stupid question to ask and if you could recommend some literature which explains this a bit more I would be happy aswell. I also would like to increase the cell number in the bottom box but I am not able to achieve it. So far I tried to merge the both boxes with mergeparis and the master and slave condition with no sucess... Is even possible to have a different number of cells in one box than in the other?

Many thanks already in advance!!

Best
fid