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[snappyHexMesh] Multiregion mesh - issues at edges

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Old   June 29, 2020, 06:56
Default Multiregion mesh - issues at edges
  #1
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Thangasivam
Join Date: Sep 2012
Location: India
Posts: 4
Rep Power: 9
namsivag is on a distinguished road
Hello all,
I am trying to create fluid and solid meshes (including interface) using snappyHexMesh v1912 for a CHT simulation. I want to study the Heat Transfer between fluid and solid pipe.
I have issues at the highlighted locations in the attached images.
Please give your suggestions to improve. I could not find where I am committing a mistake.
Thanks a lot in advance.
Cheers, Sivam

I codes and values I am using.
BlockMeshDict
Code:
scale 1; // convertToMeters does nothing in this case, 0.1 would shrink it by 10x 

vertices   // (x y z)
(
(   -0.0150 -0.0130 -0.0130  )   // in metres // vertex : 0
(   0.0550  -0.0130 -0.0130  )   // in metres // vertex : 1
(   0.0550 0.0130  -0.0130  )   // in metres // vertex : 2
(   -0.0150 0.0130  -0.0130  )   // in metres // vertex : 3
(   -0.0150 -0.0130 0.0130   )   // in metres // vertex : 4
(   0.0550  -0.0130 0.0130   )   // in metres // vertex : 5
(   0.0550 0.0130 0.0130   )   // in metres // vertex : 6
(   -0.0150 0.0130 0.0130   )   // in metres // vertex : 7
);

blocks          
( //                         Divisions 
hex (0 1 2 3 4 5 6 7) baseMesh (46 17 17)   simpleGrading (1 1 1)
);

edges           
(
);

patches         // Boundaries or faces
(               
);

mergePatchPairs
(
  );
topoSetDict
Code:
actions
(
// outside Cylinder Cell set
    {
        name solidCellSet;
        type cellSet;
        action new;
        source surfaceToCell;
        sourceInfo
        {
            file "constant/triSurface/solid.stl";
            // use closed surface inside/outside
            // test (ignores includeCut, outsidePoints)
            useSurfaceOrientation false;
            outsidePoints   ((0.01 0 0));   // definition of outside
            includeCut      true;           // cells cut by surface
            includeInside   false;          // cells not on outside of surf
            includeOutside  false;          // cells on outside of surf
            nearDistance    -1;             // cells with centre near surf (set to -1 if not used)
            curvature       0.9;            // cells within nearDistance and near surf curvature (set to -100 if not used)
        }
    }
// outside Cylinder Zone set
    {
        name    solidZone;
        type    cellZoneSet;
        action  new;
        source  setToCellZone;
        sourceInfo
        {
            set solidCellSet; 
        }
    }
// inside Cylinder Cell set
    {
        name fluidCellSet;
        type cellSet;
        action new;
        source surfaceToCell;
        sourceInfo
        {
            file "./constant/triSurface/fluid.stl";
            // use closed surface inside/outside
            // test (ignores includeCut, outsidePoints)
            useSurfaceOrientation false;
            outsidePoints   ((0.01 0 0));   // definition of outside
            includeCut      true;           // cells cut by surface
            includeInside   false;          // cells not on outside of surf
            includeOutside  false;          // cells on outside of surf
            nearDistance    -1;             // cells with centre near surf (set to -1 if not used)
            curvature       0.9;            // cells within nearDistance and near surf curvature (set to -100 if not used)
        }
    }
// inside Cylinder Zone set
    {
        name    fluidZone;
        type    cellZoneSet;
        action  new;
        source  setToCellZone;
        sourceInfo
        {
            set fluidCellSet; 
        }
    }
// combine fluidCell + solidCell set
    {
        name    fluidSolidSet;
        type    cellSet;
        action  new;
        source cellToCell;
        sourceInfo
        {
            set solidCellSet;
            set fluidCellSet;
        }
    }
// invert to get the remaining Set
    {
        name    fluidSolidSet;
        type    cellSet;
        action  invert;
    }
// remaining set to remaining zone
    {
        name    baseZone;
        type    cellZoneSet;
        action  new;
        source  setToCellZone;
        sourceInfo
        {
            set fluidSolidSet;
        }
    }
// remove the remaining zone    
    {
        name    baseZone;
        type    cellZoneSet;
        action  remove;
    }
 );
surfaceFeatureExtractDict
Code:
inlet.stl
    {
        extractionMethod    extractFromSurface;
        extractFromSurfaceCoeffs
        {includedAngle   150;}
        writeObj                no;
    } 
fluid.stl
    {
        extractionMethod    extractFromSurface;
        extractFromSurfaceCoeffs
        {includedAngle   150;}
        writeObj                no;
    }
fluidOuter.stl
    {
        extractionMethod    extractFromSurface;
        extractFromSurfaceCoeffs
        {includedAngle   150;}
        writeObj                no;
    }    
outlet.stl
    {
        extractionMethod    extractFromSurface;
        extractFromSurfaceCoeffs
        {includedAngle   150;}
        writeObj                no;
    }  
solid.stl
    {
        extractionMethod    extractFromSurface;
        extractFromSurfaceCoeffs
        {includedAngle   150;}
        writeObj                no;
    } 
solidInner.stl
    {
        extractionMethod    extractFromSurface;
        extractFromSurfaceCoeffs
        {includedAngle   150;}
        writeObj                no;
    }  
solidOuter.stl
    {
        extractionMethod    extractFromSurface;
        extractFromSurfaceCoeffs
        {includedAngle   150;}
        writeObj                no;
    }      
inletPipe.stl
    {
        extractionMethod    extractFromSurface;
        extractFromSurfaceCoeffs
        {includedAngle   150;}
        writeObj                no;
    }      
     writeFeatureEdgeMesh    yes;
snappyHexMeshDict
Code:
castellatedMesh true;    // make basic mesh ?
snap            true;    // decide to snap back to surface ?
addLayers       true;    // decide to add viscous layers ?
// singleRegionName false;  // Optional

geometry
{
    fluid.stl     {type triSurfaceMesh; name fluid ; }
    // fluid.stl {type triSurfaceMesh;
    // regions      {fluid {name fluid;}}}

    solid.stl    {type triSurfaceMesh; name solid; }
    // solid.stl {type triSurfaceMesh;
    // regions      {solid {name solid;}}}

    // inlet.stl {type triSurfaceMesh;
    // regions      {inlet {name inlet;}}}

    // outlet.stl {type triSurfaceMesh;
    // regions      {outlet {name outlet;}}}

    // inletPipe.stl {type triSurfaceMesh;
    // regions      {inletPipe {name inletPipe;}}}    

    
    inlet.stl      {type triSurfaceMesh; name inlet     ; }
    outlet.stl     {type triSurfaceMesh; name outlet    ; }
    inletPipe.stl  {type triSurfaceMesh; name inletPipe ; }
    fluidOuter.stl {type triSurfaceMesh; name fluidOuter ; }
    solidInner.stl {type triSurfaceMesh; name solidInner ; }
};

castellatedMeshControls
{
    maxLocalCells 10000000;
    maxGlobalCells 20000000;
    minRefinementCells 10;//10;
    maxLoadUnbalance 0.10;//0.10;
    nCellsBetweenLevels 4;//4;

    features // taken from STL from each .eMesh file created by "SurfaceFeatureExtract" command
    (
        {file "fluid.eMesh";      level 2;}
        {file "solid.eMesh";      level 2;}
        {file "outlet.eMesh";     level 2;}
        {file "inlet.eMesh";      level 2;}
        {file "inletPipe.eMesh";  level 2;}
        {file "fluidOuter.eMesh";  level 2;}
        {file "solidInner.eMesh";  level 2;}
    );

    refinementSurfaces // Surface-wise min and max refinement level
    {
        fluid{
            level (2 2); // (min max )
            faceZone fluid;
            cellZone fluid;
            cellZoneInside inside;            
            }

        solid{
            level (2 2);
            faceZone solid;
            cellZone solid;
            cellZoneInside inside;                        
            }

        inlet     { level ( 1 2 ) ; patchInfo { type patch; } } 
        outlet    { level ( 1 2 ) ; patchInfo { type patch; } } 
        inletPipe { level ( 1 2 ) ; patchInfo { type wall;  } }
        // fluidOuter { level ( 1 2 ) ; patchInfo { type wall;  } }
        // solidInner { level ( 1 2 ) ; patchInfo { type wall;  } }
    }

    resolveFeatureAngle 10;//20;//30;//80
    refinementRegions        // In descending levels of fine-ness
    {
        fluid        {mode inside; levels ((2 1));}
        solid        {mode inside; levels ((2 1));}
    }
    locationInMesh (0.01 0.0 0.0); // in metres

    // locationsInMesh // in metres
    // (
    //     (( 0.0  0.0     0.0) inside)
    //     (( 3e-3 6.5e-3  0.0) outside)
    // );

    allowFreeStandingZoneFaces true;
}

snapControls
{
    nFaceSplitInterval  5;
    nSmoothPatch 5;
    tolerance    1.0;//4.0;
    nSolveIter   60;//300;//60;
    nRelaxIter   5;//10;//5;
    nFeatureSnapIter 10;//15; // default is 10
    implicitFeatureSnap false; // default is false - detects without doing surfaceFeatureExtract
    explicitFeatureSnap true; // default is true
    multiRegionFeatureSnap true; // deafault is false - detects features between multiple surfaces
}

addLayersControls
{
    relativeSizes true;
    layers
    {
       fluid_slave
        {
         nSurfaceLayers 3; // was 5
        }
    }
    expansionRatio 1.5;
    finalLayerThickness 5e-3;
    minThickness 5e-4;
    nGrow 0;//was 1;
    featureAngle 110;//85;//30;
    nRelaxIter 5;//3;
    nSmoothSurfaceNormals 4;//1;
    nSmoothNormals 3;
    nSmoothThickness 10;
    maxFaceThicknessRatio 0.5;
    maxThicknessToMedialRatio 0.2;//0.3;
    minMedianAxisAngle 90;//130;
    nBufferCellsNoExtrude 0;
    nLayerIter 50;
    detectExtrusionIsland true;    
}
meshQualityControls
{
    maxNonOrtho 65;
    maxBoundarySkewness 20;
    maxInternalSkewness 4;
    maxConcave 80;
    minFlatness 0.5;
    minVol 1e-13;
    minArea -1;
    minTwist 0.02;
    minDeterminant 0.001;
    minFaceWeight 0.02;
    minVolRatio 0.01;
    minTetQuality 1e-30;
    minTriangleTwist -1;
    nSmoothScale 4;
    errorReduction 0.75;
}
debug 0;
writeFlags
(
    scalarLevels
    layerSets
    layerFields     // write volScalarField for layer coverage
);
mergeTolerance 1E-6;
Attached Images
File Type: jpg 01.jpg (64.4 KB, 8 views)
File Type: jpg 02.jpg (64.2 KB, 9 views)
File Type: jpg 04.jpg (72.6 KB, 9 views)
File Type: jpg 05.jpg (84.0 KB, 10 views)
File Type: jpg 06.jpg (84.3 KB, 7 views)
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Old   June 29, 2020, 10:53
Default
  #2
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Join Date: Jun 2020
Location: UK
Posts: 11
Rep Power: 2
Rango is on a distinguished road
Hi,


Just a few observations that may help:
  1. Turn off the "addLayers" option and see if you can get a sharp edge at inlet.
  2. Edit "refinementSurfaces" section to
    Code:
    refinementSurfaces // Surface-wise min and max refinement level
        {
            fluid{
                level (0 0); // (min max )
                faceZone fluid;
                cellZone fluid;
                cellZoneInside inside;            
                }
    
            solid{
                level (0 0);
                faceZone solid;
                cellZone solid;
                cellZoneInside inside;                        
                }
    
            inlet     { level (2 2 ) ; patchInfo { type patch; } } 
            outlet    { level ( 2 2 ) ; patchInfo { type patch; } } 
          
        }
    and "refinementRegions" section to
    Code:
    refinementRegions        // In descending levels of fine-ness
        {
            fluid        {mode inside; levels ((2 2));}
            solid        {mode inside; levels ((2 2));}
        }
  3. Do you need to include "featureEdge (eMesh files)" for every single "stl" file that you have?
  4. Increase "resolveFeatureAngle" to 60.
  5. Turn off "multiRegionFeatureSnap".
Cheers
Rango is offline   Reply With Quote

Old   June 30, 2020, 01:32
Default Wow.. Partial Success
  #3
New Member
 
Thangasivam
Join Date: Sep 2012
Location: India
Posts: 4
Rep Power: 9
namsivag is on a distinguished road
Dear Rango,
Thanks for the values. Sharp edges are generated at inlet of fluid domain.

Your query :
Do you need to include "featureEdge (eMesh files)" for every single "stl" file that you have?
I thought that "featureEdge (eMesh files)" might improve the meshes at the edges.

Some more help needed.
A. I have some issues at the edges on fluid and solid surfaces at interface starting location. I have highlighted on the attached images.
B. I would like to get rid of the baseMesh interfaces with the solid and fluid surfaces. I have highlighted on the attached images.

Thanks again.
Cheers, Sivam

I am sharing the codes and images.

Code:
castellatedMesh true;    // make basic mesh ?
snap            true;    // decide to snap back to surface ?
addLayers       false;    // decide to add viscous layers ?

geometry
{
    fluid.stl    {type triSurfaceMesh; name fluid; }
    solid.stl    {type triSurfaceMesh; name solid; }

    inlet.stl      {type triSurfaceMesh; name inlet     ; }
    outlet.stl     {type triSurfaceMesh; name outlet    ; }
    inletPipe.stl  {type triSurfaceMesh; name inletPipe ; }
};

castellatedMeshControls
{
    maxLocalCells  10000000;
    maxGlobalCells 20000000;
    minRefinementCells 10;
    maxLoadUnbalance 0.10;
    nCellsBetweenLevels 4;

    features // taken from STL from each .eMesh file created by "SurfaceFeatureExtract" command
    (
        {file "fluid.eMesh";      level 2;}
        {file "solid.eMesh";      level 2;}
        {file "outlet.eMesh";     level 2;}
        {file "inlet.eMesh";      level 2;}
        {file "inletPipe.eMesh";  level 2;}
    );

    refinementSurfaces // Surface-wise min and max refinement level
    {
        fluid{
            level (0 0); // (min max )
            faceZone fluid;
            cellZone fluid;
            cellZoneInside inside;            
            }

        solid{
             level (0 0);
            faceZone solid;
            cellZone solid;
            cellZoneInside inside;                        
            }

        inlet     { level ( 2 2 ) ; patchInfo { type patch; } } 
        outlet    { level ( 2 2 ) ; patchInfo { type patch; } } 
        // inletPipe { level ( 1 2 ) ; patchInfo { type wall;  } }
    }

     resolveFeatureAngle 60;
    refinementRegions      // In descending levels of fine-ness
    {
        fluid        {mode inside; levels ((2 2));}
        solid        {mode inside; levels ((2 2));}
    }
    locationInMesh (0.01 0.0 0.0); // in metres
    allowFreeStandingZoneFaces true;
}

snapControls
{
    nFaceSplitInterval  5;
    nSmoothPatch        5;
    tolerance         1.0; // 4.0;
    nSolveIter         60; // 300;
    nRelaxIter          5; // 10;
    nFeatureSnapIter   10; // default is 10
    
    implicitFeatureSnap    false; // default is false - detects without doing surfaceFeatureExtract
    explicitFeatureSnap    true;  // default is true
     multiRegionFeatureSnap false;


 }

addLayersControls
{
    relativeSizes true;
    layers
    {
       fluid_slave
        {
         nSurfaceLayers 3;
        }
    }
    expansionRatio            1.5;
    finalLayerThickness      5e-3;
    minThickness             5e-4;
    nGrow                       0;//was 1;
    featureAngle              110;//85;//30;
    nRelaxIter                  5;//3;
    nSmoothSurfaceNormals       4;//1;
    nSmoothNormals              3;
    nSmoothThickness           10;
    maxFaceThicknessRatio     0.5;
    maxThicknessToMedialRatio 0.2;//0.3;
    minMedianAxisAngle         90;//130;
    nBufferCellsNoExtrude       0;
    nLayerIter                 50;
    detectExtrusionIsland    true;    
}
meshQualityControls
{
    maxNonOrtho         65;
    maxBoundarySkewness 20;
    maxInternalSkewness  4;
    maxConcave          80;
    
    minFlatness        0.5;
    minVol           1e-13;
    minArea             -1;
    minTwist          0.02;
    
    minDeterminant   0.001;
    minFaceWeight     0.02;
    minVolRatio       0.01;
    minTetQuality    1e-30;
    
    minTriangleTwist    -1;
    nSmoothScale         4;
    errorReduction    0.75;
}
debug 0;
writeFlags
(
    scalarLevels
    layerSets
    layerFields     // write volScalarField for layer coverage
);
mergeTolerance 1E-6;
Attached Images
File Type: jpg a1.jpg (195.5 KB, 8 views)
File Type: jpg a2.jpg (125.6 KB, 7 views)
File Type: jpg a3.jpg (55.0 KB, 8 views)

Last edited by namsivag; June 30, 2020 at 01:37. Reason: forgot to attach
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