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Boundary layer in a pipe

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Old   September 15, 2011, 09:02
Default Boundary layer in a pipe
  #1
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clement
Join Date: May 2011
Location: München
Posts: 12
Rep Power: 5
Clementhuon is on a distinguished road
Hi OpenFOAMer,

I'm actually trying to mesh a cabin for a HVAC problem with the SHM. But after a lot of attempts I don't succed in creating my boundary layer in the entire pipe system. You will find enclosed a cross section of the pipe and a copy of my SHMdict file. You will see that when the curvature of my pipe increase, the BL desappear.

If somebody get an idea .... I allready read a lot of topic on the subject but found any explanation.

Thanks

Clement

PHP Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  1.7.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    
version     2.0;
    
format      ascii;
    class       
dictionary;
    
object      snappyHexMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
// Which of the steps to run
    
castellatedMesh 1;
    
snap            1;
    
addLayers       1;


// Geometry. Definition of all surfaces. All surfaces are of class
// searchableSurface.
// Surfaces are used
// - to specify refinement for any mesh cell intersecting it
// - to specify refinement for any mesh cell inside/outside/near
// - to 'snap' the mesh boundary to the surface

geometry
{
    
inlet.stl{
        
type triSurfaceMesh;
        
name inlet;}
    
outlet.stl{
        
type triSurfaceMesh;
        
name outlet;}
    
pipe.stl{
        
type triSurfaceMesh;
        
name pipe;}
    
inlay.stl{
        
type triSurfaceMesh;
        
name inlay;}
    
cabin-roof.stl{
        
type triSurfaceMesh;
        
name cabin-roof;}
    
cabin-side.stl{
        
type triSurfaceMesh;
        
name cabin-side;}
    
cabin-front.stl{
        
type triSurfaceMesh;
        
name cabin-front;}
    
cabin-floor.stl{
        
type triSurfaceMesh;
        
name cabin-floor;}
    
cabin-back.stl{
        
type triSurfaceMesh;
        
name cabin-back;}
    
refine-roof.stl{
        
type triSurfaceMesh;
        
name refine-roof;}
    
refine-panel-top.stl{
        
type triSurfaceMesh;
        
name refine-panel-top;}
    
panel.stl{
        
type triSurfaceMesh;
        
name panel;}
};

// Settings for the castellatedMesh generation.
castellatedMeshControls
{
    
// Refinement parameters
    // ~~~~~~~~~~~~~~~~~~~~~

    // If local number of cells is >= maxLocalCells on any processor
    // switches from from refinement followed by balancing
    // (current method) to (weighted) balancing before refinement.
    
maxLocalCells 200000000;

    
// Overall cell limit (approximately). Refinement will stop immediately
    // upon reaching this number so a refinement level might not complete.
    // Note that this is the number of cells before removing the part which
    // is not 'visible' from the keepPoint. The final number of cells might
    // actually be a lot less.
    
maxGlobalCells 200000000;

    
// The surface refinement loop might spend lots of iterations refining just a
    // few cells. This setting will cause refinement to stop if <= minimumRefine
    // are selected for refinement. Note: it will at least do one iteration
    // (unless the number of cells to refine is 0)
    
minRefinementCells 2000;

    
// Allow a certain level of imbalance during refining
    // (since balancing is quite expensive)
    // Expressed as fraction of perfect balance (= overall number of cells /
    // nProcs). 0=balance always.
   // maxLoadUnbalance 0.1;

    // Number of buffer layers between different levels.
    // 1 means normal 2:1 refinement restriction, larger means slower
    // refinement.
    
nCellsBetweenLevels 5;

    
// Explicit feature edge refinement
    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    // Specifies a level for any cell intersected by its edges.
    // This is a featureEdgeMesh, read from constant/triSurface for now.
    
features
    
(
        {
            
file "inlet.eMesh";
            
level 3;
        }
        {
            
file "outlet.eMesh";
            
level 3;
        }
        {
            
file "pipe.eMesh";
            
level 3;
        }
        {
            
file "inlay.eMesh";
            
level 3;
        }
        {
            
file "cabin-roof.eMesh";
            
level 3;
        }
        {
            
file "cabin-side.eMesh";
            
level 3;
        }
        {
            
file "cabin-front.eMesh";
            
level 3;
        }
        {
            
file "cabin-floor.eMesh";
            
level 3;
        }
        {
            
file "cabin-back.eMesh";
            
level 3;
        }
        {
            
file "refine-roof.eMesh";
            
level 3;
        }
        {
            
file "refine-panel-top.eMesh";
            
level 3;
        }
        {
            
file "panel.eMesh";
            
level 3;
        }
    );

    
// Surface based refinement
    // ~~~~~~~~~~~~~~~~~~~~~~~~

    // Specifies two levels for every surface. The first is the minimum level,
    // every cell intersecting a surface gets refined up to the minimum level.
    // The second level is the maximum level. Cells that 'see' multiple
    // intersections where the intersections make an
    // angle > resolveFeatureAngle get refined up to the maximum level.

    
refinementSurfaces
    
{
        
inlet{
            
// Surface-wise min and max refinement level
            
level (5 5);}
        
outlet{
            
// Surface-wise min and max refinement level
            
level (1 1);}
        
pipe{
            
// Surface-wise min and max refinement level
            
level (5 5);}
        
inlay{
            
// Surface-wise min and max refinement level
            
level (6 6);}
        
cabin-roof{
            
// Surface-wise min and max refinement level
            
level (1 1);}
        
cabin-side{
            
// Surface-wise min and max refinement level
            
level (1 1);}
        
cabin-front{
            
// Surface-wise min and max refinement level
            
level (1 1);}
        
cabin-floor{
            
// Surface-wise min and max refinement level
            
level (1 1);}
        
cabin-back{
            
// Surface-wise min and max refinement level
            
level (1 1);}
        
refine-roof{
            
// Surface-wise min and max refinement level
            
level (6 6);}
        
refine-panel-top{
            
// Surface-wise min and max refinement level
            
level (6 6);}
        
panel{
            
// Surface-wise min and max refinement level
            
level (1 1);}
    }

    
// Resolve sharp angles
    
resolveFeatureAngle 10;

    
// Region-wise refinement
    // ~~~~~~~~~~~~~~~~~~~~~~

    // Specifies refinement level for cells in relation to a surface. One of
    // three modes
    // - distance. 'levels' specifies per distance to the surface the
    //   wanted refinement level. The distances need to be specified in
    //   descending order.
    // - inside. 'levels' is only one entry and only the level is used. All
    //   cells inside the surface get refined up to the level. The surface
    //   needs to be closed for this to be possible.

    // - outside. Same but cells outside.

    
refinementRegions
    
{
    }

    
// Mesh selection
    // ~~~~~~~~~~~~~~

    // After refinement patches get added for all refinementSurfaces and
    // all cells intersecting the surfaces get put into these patches. The
    // section reachable from the locationInMesh is kept.
    // NOTE: This point should never be on a face, always inside a cell, even
    // after refinement.
    
locationInMesh (-1864.72 574.182 2774.74);

    
// Whether any faceZones (as specified in the refinementSurfaces)
    // are only on the boundary of corresponding cellZones or also allow
    // free-standing zone faces. Not used if there are no faceZones.
    
allowFreeStandingZoneFaces true;
}

// Settings for the snapping.
snapControls
{
    
//- Number of patch smoothing iterations before finding correspondence
    //  to surface
    
nSmoothPatch 5;

    
//- Relative distance for points to be attracted by surface feature point
    //  or edge. True distance is this factor times local
    //  maximum edge length.
    
tolerance 1.0;

    
//- Number of mesh displacement relaxation iterations.
    
nSolveIter 300;

    
//- Maximum number of snapping relaxation iterations. Should stop
    //  before upon reaching a correct mesh.
    
nRelaxIter 15;

    
//- Highly experimental and wip: number of feature edge snapping
    //  iterations. Leave out altogether to disable.
    
nFeatureSnapIter 20;
}

// Settings for the layer addition.
addLayersControls
{
    
// Are the thickness parameters below relative to the undistorted
    // size of the refined cell outside layer (true) or absolute sizes (false).
    
relativeSizes true;

    
// Per final patch (so not geometry!) the layer information
    
layers
    
{
        
inlet_inlet{
          
nSurfaceLayers 2;};
        
pipe_pipe{
          
nSurfaceLayers 2;};
        
inlay_inlay{
          
nSurfaceLayers 2;};
        
refine-roof_refine-roof{
          
nSurfaceLayers 2;};
        
refine-panel-top_refine-panel-top{
          
nSurfaceLayers 2;};
    }

    
// Expansion factor for layer mesh
    
expansionRatio 1.2;

    
//- Wanted thickness of final added cell layer. If multiple layers
    //  is the thickness of the layer furthest away from the wall.
    //  See relativeSizes parameter.
    
finalLayerThickness 0.8;

    
//- Minimum thickness of cell layer. If for any reasn layer
    //  cannot be above minThickness do not add layer.
    //  Relative to undistorted size of cell outside layer.
    
minThickness 0.05;

    
//- If points get not extruded do nGrow layers of connected faces that are
    //  also not grown. This helps convergence of the layer addition process
    //  close to features.
    
nGrow 0;

    
// Advanced settings

    //- When not to extrude surface. 0 is flat surface, 90 is when two faces
    //  make straight angle.
    
featureAngle 30;

    
//- Maximum number of snapping relaxation iterations. Should stop
    //  before upon reaching a correct mesh.
    
nRelaxIter 20;

    
// Number of smoothing iterations of surface normals
    
nSmoothSurfaceNormals 20;

    
// Number of smoothing iterations of interior mesh movement direction
    
nSmoothNormals 20;

    
// Smooth layer thickness over surface patches
    
nSmoothThickness 10;

    
// Stop layer growth on highly warped cells
    
maxFaceThicknessRatio 0.1;

    
// Reduce layer growth where ratio thickness to medial
    // distance is large
    
maxThicknessToMedialRatio 0.05;

    
// Angle used to pick up medial axis points
    
minMedianAxisAngle 60;

    
// Create buffer region for new layer terminations
    
nBufferCellsNoExtrude 0;

    
// Overall max number of layer addition iterations
    
nLayerIter 120;

    
nRelaxedIter 60;
}

// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
    
//- Maximum non-orthogonality allowed. Set to 180 to disable.
    
maxNonOrtho 65;

    
//- Max skewness allowed. Set to <0 to disable.
    
maxBoundarySkewness 20;
    
maxInternalSkewness 4;

    
//- Max concaveness allowed. Is angle (in degrees) below which concavity
    //  is allowed. 0 is straight face, <0 would be convex face.
    //  Set to 180 to disable.
    
maxConcave 80;

    
//- Minimum projected area v.s. actual area. Set to -1 to disable.
    
minFlatness 0.5;

    
//- Minimum pyramid volume. Is absolute volume of cell pyramid.
    //  Set to a sensible fraction of the smallest cell volume expected.
    //  Set to very negative number (e.g. -1E30) to disable.
    
minVol 1e-06;

    
//- Minimum quality of the tet formed by the face-centre
    //  and variable base point minimum decomposition triangles and
    //  the cell centre. This has to be a positive number for tracking
    //  to work. Set to very negative number (e.g. -1E30) to
    //  disable.
    //     <0 = inside out tet,
    //      0 = flat tet
    //      1 = regular tet
    
minTetQuality 1e-9;

    
//- Minimum face area. Set to <0 to disable.
    
minArea 0.0001;

    
//- Minimum face twist. Set to <-1 to disable. dot product of face normal
    //- and face centre triangles normal
    
minTwist 0.02;

    
//- minimum normalised cell determinant
    //- 1 = hex, <= 0 = folded or flattened illegal cell
    
minDeterminant 0.001;

    
//- minFaceWeight (0 -> 0.5)
    
minFaceWeight 0.02;

    
//- minVolRatio (0 -> 1)
    
minVolRatio 0.01;

    
//must be >0 for Fluent compatibility
    
minTriangleTwist -1;

    
// Advanced

    //- Number of error distribution iterations
    
nSmoothScale 4;
    
//- amount to scale back displacement at error points
    
errorReduction 0.75;
}

// Advanced

// Flags for optional output
// 0 : only write final meshes
// 1 : write intermediate meshes
// 2 : write volScalarField with cellLevel for postprocessing
// 4 : write current intersections as .obj files
debug 0;

// Merge tolerance. Is fraction of overall bounding box of initial mesh.
// Note: the write tolerance needs to be higher than this.
mergeTolerance 1E-6;

// ************************************************************************* // 
[IMG]file:///tmp/moz-screenshot.png[/IMG]
Attached Images
File Type: jpg pipe_cross_section.jpg (43.3 KB, 109 views)
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Old   September 22, 2011, 06:38
Default No idea ????
  #2
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clement
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I tried a lot of combination for the parameters and didn't find any solution. Could someone help me ? If you don't have enough information I can give further description of my problem ........

Thanks

Clement
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Old   March 11, 2012, 11:53
Default
  #3
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Daniele Vicario
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Hi, I've got the same problem. Have you find a solution ?

Daniele
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Old   March 11, 2012, 13:51
Default
  #4
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Daniele Vicario
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Looking other threads it seems to be a naming problem, but I already tried several changes in the addLayersControls / layers setup.

Here is my SHMDict:

Code:
// Which of the steps to run
castellatedMesh true;
snap            true;
addLayers       true;
 
// Geometry. Definition of all surfaces. All surfaces are of class
// searchableSurface.
// Surfaces are used
// - to specify refinement for any mesh cell intersecting it
// - to specify refinement for any mesh cell inside/outside/near
// - to 'snap' the mesh boundary to the surface
geometry
{
    tubo.stl
    {
        type triSurfaceMesh;
        name tubo;
        regions 
        {
            tubo
            {
                name tubo;
            }
        }
    }
 
    inlet.stl
    {
        type triSurfaceMesh;
        name inlet;
        regions
        {
            inlet
            {
                name inlet;
            }
        }
    }
 
    outlet.stl
    {
        type triSurfaceMesh;
        name outlet;
        regions
        {
            outlet
            {
                name outlet;
            }
        }
 
    }
    //refinementBox
    //{
    //    type searchableBox;
    //    min (-0.01 -0.01 -0.31);
    //    max ( 0.01  0.01 0.01);
    //}
};
 
// Settings for the castellatedMesh generation.
castellatedMeshControls
{
    // Refinement parameters
    // ~~~~~~~~~~~~~~~~~~~~~
    // If local number of cells is >= maxLocalCells on any processor
    // switches from from refinement followed by balancing
    // (current method) to (weighted) balancing before refinement.
    maxLocalCells 100000;
    // Overall cell limit (approximately). Refinement will stop immediately
    // upon reaching this number so a refinement level might not complete.
    // Note that this is the number of cells before removing the part which
    // is not 'visible' from the keepPoint. The final number of cells might
    // actually be a lot less.
    maxGlobalCells 2000000;
    // The surface refinement loop might spend lots of iterations refining just a
    // few cells. This setting will cause refinement to stop if <= minimumRefine
    // are selected for refinement. Note: it will at least do one iteration
    // (unless the number of cells to refine is 0)
    minRefinementCells 10;
    // Allow a certain level of imbalance during refining
    // (since balancing is quite expensive)
    // Expressed as fraction of perfect balance (= overall number of cells /
    // nProcs). 0=balance always.
    maxLoadUnbalance 0.10;
 
    // Number of buffer layers between different levels.
    // 1 means normal 2:1 refinement restriction, larger means slower
    // refinement.
    nCellsBetweenLevels 5;
 
    // Explicit feature edge refinement
    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    // Specifies a level for any cell intersected by its edges.
    // This is a featureEdgeMesh, read from constant/triSurface for now.
    features
    (
 
 
        //{
        //    file "someLine.eMesh";
        //    level 2;
        //}
    );
 
    // Surface based refinement
    // ~~~~~~~~~~~~~~~~~~~~~~~~
    // Specifies two levels for every surface. The first is the minimum level,
    // every cell intersecting a surface gets refined up to the minimum level.
    // The second level is the maximum level. Cells that 'see' multiple
    // intersections where the intersections make an
    // angle > resolveFeatureAngle get refined up to the maximum level.
    refinementSurfaces
    {
        tubo
        {
            // Surface-wise min and max refinement level
            //level (5 6);
            level (2 3);
        }
        inlet
        {
            // Surface-wise min and max refinement level
            //level (5 6);
            level (2 3);
        }
        outlet
        {
            // Surface-wise min and max refinement level
            //level (5 6);
            level (2 3);
        }
    }
    // Resolve sharp angles
    resolveFeatureAngle 30;
 
    // Region-wise refinement
    // ~~~~~~~~~~~~~~~~~~~~~~
    // Specifies refinement level for cells in relation to a surface. One of
    // three modes
    // - distance. 'levels' specifies per distance to the surface the
    //   wanted refinement level. The distances need to be specified in
    //   descending order.
    // - inside. 'levels' is only one entry and only the level is used. All
    //   cells inside the surface get refined up to the level. The surface
    //   needs to be closed for this to be possible.
    // - outside. Same but cells outside.
    refinementRegions
    {
        //tubo
        //{
        //    mode inside;
        //    levels ((1E15 2));
        //}
    }
 
    // Mesh selection
    // ~~~~~~~~~~~~~~
    // After refinement patches get added for all refinementSurfaces and
    // all cells intersecting the surfaces get put into these patches. The
    // section reachable from the locationInMesh is kept.
    // NOTE: This point should never be on a face, always inside a cell, even
    // after refinement.
    locationInMesh (0 0 -0.2);
 
    // Whether any faceZones (as specified in the refinementSurfaces)
    // are only on the boundary of corresponding cellZones or also allow
    // free-standing zone faces. Not used if there are no faceZones.
    allowFreeStandingZoneFaces true;
}
 
// Settings for the snapping.
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 4.0;
    //- Number of mesh displacement relaxation iterations.
    //nSolveIter 0;
    nSolveIter 30;
    //- Maximum number of snapping relaxation iterations. Should stop
    //  before upon reaching a correct mesh.
    nRelaxIter 5;
    //- Highly experimental and wip: number of feature edge snapping
    //  iterations. Leave out altogether to disable.
    //  Do not use here since mesh resolution too low and baffles present
    //nFeatureSnapIter 10;
}
// Settings for the layer addition.
addLayersControls
{
    // Are the thickness parameters below relative to the undistorted
    // size of the refined cell outside layer (true) or absolute sizes (false).
    relativeSizes true;
    // Per final patch (so not geometry!) the layer information
    layers
    {
        tubo
        {
            nSurfaceLayers 5;
        }
        inlet
        {
            nSurfaceLayers 5;
        }
        outlet
        {
            nSurfaceLayers 5;
        }
    }
    // Expansion factor for layer mesh
    expansionRatio 1.0;
    //- Wanted thickness of final added cell layer. If multiple layers
    //  is the
    //  thickness of the layer furthest away from the wall.
    //  Relative to undistorted size of cell outside layer.
    //  is the thickness of the layer furthest away from the wall.
    //  See relativeSizes parameter.
    //finalLayerThickness 0.3;
    finalLayerThickness 0.1;
    //- Minimum thickness of cell layer. If for any reason layer
    //  cannot be above minThickness do not add layer.
    //  Relative to undistorted size of cell outside layer.
    minThickness 0.1;
    //minThickness 0.0005;
    //- If points get not extruded do nGrow layers of connected faces that are
    //  also not grown. This helps convergence of the layer addition process
    //  close to features.
    // Note: changed(corrected) w.r.t 17x! (didn't do anything in 17x)
    nGrow 1;
    // Advanced settings
    //- When not to extrude surface. 0 is flat surface, 90 is when two faces
    //  make straight angle.
    featureAngle 30;
    //- Maximum number of snapping relaxation iterations. Should stop
    //  before upon reaching a correct mesh.
    nRelaxIter 5;
    // Number of smoothing iterations of surface normals
    nSmoothSurfaceNormals 1;
    // Number of smoothing iterations of interior mesh movement direction
    nSmoothNormals 3;
    // Smooth layer thickness over surface patches
    nSmoothThickness 10;
    // Stop layer growth on highly warped cells
    maxFaceThicknessRatio 0.5;
    // Reduce layer growth where ratio thickness to medial
    // distance is large
    maxThicknessToMedialRatio 0.3;
    // Angle used to pick up medial axis points
    // Note: changed(corrected) w.r.t 17x! 90 degrees corresponds to 130 in 17x.
    minMedianAxisAngle 90;
 
    // Create buffer region for new layer terminations
    nBufferCellsNoExtrude 0;
 
    // Overall max number of layer addition iterations. The mesher will exit
    // if it reaches this number of iterations; possibly with an illegal
    // mesh.
    nLayerIter 50;
}
 
// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
    //- Maximum non-orthogonality allowed. Set to 180 to disable.
    maxNonOrtho 65;
    //- Max skewness allowed. Set to <0 to disable.
    maxBoundarySkewness 20;
    maxInternalSkewness 4;
    //- Max concaveness allowed. Is angle (in degrees) below which concavity
    //  is allowed. 0 is straight face, <0 would be convex face.
    //  Set to 180 to disable.
    maxConcave 80;
    //- Minimum pyramid volume. Is absolute volume of cell pyramid.
    //  Set to a sensible fraction of the smallest cell volume expected.
    //  Set to very negative number (e.g. -1E30) to disable.
    minVol 1e-13;
    //- Minimum quality of the tet formed by the face-centre
    //  and variable base point minimum decomposition triangles and
    //  the cell centre. This has to be a positive number for tracking
    //  to work. Set to very negative number (e.g. -1E30) to
    //  disable.
    //     <0 = inside out tet,
    //      0 = flat tet
    //      1 = regular tet
    minTetQuality 1e-30;
    //- Minimum face area. Set to <0 to disable.
    minArea -1;
    //- Minimum face twist. Set to <-1 to disable. dot product of face normal
    //- and face centre triangles normal
    minTwist 0.02;
    //- minimum normalised cell determinant
    //- 1 = hex, <= 0 = folded or flattened illegal cell
    minDeterminant 0.001;
    //- minFaceWeight (0 -> 0.5)
    minFaceWeight 0.02;
    //- minVolRatio (0 -> 1)
    minVolRatio 0.01;
    //must be >0 for Fluent compatibility
    minTriangleTwist -1;
 
    // Advanced
    //- Number of error distribution iterations
    nSmoothScale 4;
    //- amount to scale back displacement at error points
    errorReduction 0.75;
}
 
// Advanced
// Flags for optional output
// 0 : only write final meshes
// 1 : write intermediate meshes
// 2 : write volScalarField with cellLevel for postprocessing
// 4 : write current intersections as .obj files
debug 0;
 
// Merge tolerance. Is fraction of overall bounding box of initial mesh.
// Note: the write tolerance needs to be higher than this.
mergeTolerance 1e-6;
 
// ************************************************************************* //
Thanks for any help.

Daniele
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Old   March 12, 2012, 04:08
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Daniele Vicario
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After some trial I've got a SHMDict that works creating layers.
Note: maybe it was just me that checked the mesh in Parafoam looking just at inlet surface (without cutting the pipe#. I was expecting a layering on this surface too.

The problem now is on the terminal surfaces. The layers are mergin all togheter in a single cell #see picture). I red that featureAngle can modify this behavior. I'll try it but... Any hint ?
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Old   March 12, 2012, 10:05
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Daniele Vicario
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Using that mesh give me a problem in solving an Interfoam laminar case.

I don't know whether continue this thread here or move into the solvers forum.

Anyway, as you can see in the pictures, the irregular mesh causes some high pressure spots. The simulation is still going, no crash at the moment.

Any hint how to improve the mesh ?

Daniele
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Old   March 12, 2012, 14:41
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Daniele Vicario
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I hopefully found a solution at Boundary layers on an inlet/outlet for a pipe
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