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[snappyHexMesh] Inflation Layers stop at the corners

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Old   December 1, 2023, 12:22
Default Inflation Layers stop at the corners
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To familiarise myself with OpenFoam I am trying to run a simple case through a meso-scale rectangular duct (3D simulation). I am meshing using snappyHexMesh, and I can snap to the geometry and create refinement regions. When it comes to the add layer controls, I can add inflation layers, but the inflation does not extend to the corners of the duct (see attached snapshot).


My snappyHexMeshDict is as follows:


FoamFile
{
version 2.0;
format ascii;
class dictionary;
object snappyHexMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

// Which of the steps to run
castellatedMesh true;
snap true;
addLayers true;

//Surface and Region Refinement
RS 2; // Refine surfaces
RZ 2; // Refinement

geometry
{
// .stl file created using FreeCad
inlet.stl
{
type triSurfaceMesh;
name inlet; //patch name
}
outlet.stl
{
type triSurfaceMesh;
name outlet;
}
walls.stl
{
type triSurfaceMesh;
name walls;
}

refinementBox
{
type box;
min (0 1 1);
max (270 9 2);
}
};



castellatedMeshControls
{

maxLocalCells 100000;

maxGlobalCells 7000000;

minRefinementCells 10;

maxLoadUnbalance 0.10;

nCellsBetweenLevels 3;

features
(
{
file "inlet.eMesh";
level 1;
}
{
file "outlet.eMesh";
level 1;
}
{
file "walls.eMesh";
level 3; //$RS
}
);

refinementSurfaces
{
"inlet"
{
level (1 1);
patchInfo
{
type patch;
}


}
"outlet"
{
level (1 1);
patchInfo
{
type patch;
}

}
"walls"
{
level (3 3);
patchInfo
{
type wall;
}

faceType internal;
}
}

resolveFeatureAngle 15; // I have varied this to try and solve the issue

planarAngle 15;

refinementRegions
{
refinementBox
{
mode inside;
levels ((1 $RZ));
}


}



gapLevel (10 20 1.5);
gapMode inside;


locationInMesh (135 5 1.5); // centre of domain

allowFreeStandingZoneFaces true;

useLeakClosure true;

handleSnapProblems false;

useTopologicalSnapDetection false;

interfaceRefine false;

}


snapControls
{

nSmoothPatch 5;

nSmoothInternal 2;

tolerance 2.0;

nSolveIter 30;

nRelaxIter 10; //5

nFeatureSnapIter 10;

implicitFeatureSnap false;

explicitFeatureSnap true;

multiRegionFeatureSnap false;

nFaceSplitInterval -1;

strictRegionSnap false;

}


addLayersControls
{
relativeSizes true;


layers
{
walls
{
nSurfaceLayers 5;
}
}

expansionRatio 1.2;

finalLayerThickness 0.5;

minThickness 0.01; // I've reduced this to try and solve the issue

nGrow 0;

featureAngle 90; // I have also reduced and increased this

slipFeatureAngle 30; // I have also reduced and increased this


nRelaxIter 5;

nSmoothSurfaceNormals 1;

nSmoothNormals 3;

nSmoothThickness 10;

maxFaceThicknessRatio 0.2;

maxThicknessToMedialRatio 0.6;

minMedialAxisAngle 90;

nBufferCellsNoExtrude 0;

nLayerIter 50;

nRelaxedIter 20;
}


meshQualityControls
{
#include "meshQualityDict"
relaxed
{

maxNonOrtho 75;
}


nSmoothScale 4;
errorReduction 0.75;
minVol 1e-10;
minTetQuality 1e-10;
}

setFormat ensight;

writeFlags
(
scalarLevels
layerSets
layerFields
);

mergeTolerance 1e-6;


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


I've deeted many comments from the above Dict, so may have accidentally deleted some closing '{'. I have modified this dict from the motorbike tutorial as a base, but then went through the entire snappyHexMesh section in the documentation on openFoam.org to add other settings.


Any help to make the mesh finer around the corners and make the inflation layers smoother around the inner perimeter of the mesh would be gratefully appreciated.


Cheers.
Attached Images
File Type: jpg Screenshot 2023-12-01 at 15.38.30.jpg (128.5 KB, 18 views)
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Old   December 4, 2023, 03:44
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Normally, it should work with the featureAngle setting of >= 90 which you have set already. This appears to be at a boundary face. Have you checked its also collapsing further inside the mesh, e.g. if you make a slice or clip halfway through the geometry?
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Old   December 4, 2023, 08:04
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Thank you for your suggestion, sorry I should have shared an image of a clip also. The elongated features are conserved throughout the mesh structure, I've attached an updated picture.


I must have suppressed the inflation from the wall features at the interfaces between the adjoining walls; it seems to be applying inflation at each flat surface, but individually and then merging the surfaces together, while preserving the width of the cells adjacent to the walls.
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File Type: jpg Screenshot 2023-12-04 at 11.53.05.jpg (66.8 KB, 12 views)
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Old   December 4, 2023, 08:42
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I would probably try absolute sizes (relativeSizes=False) and then increasing the featureAngle to 100, 110, 120 and see what happens.
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