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[snappyHexMesh] Unable to capture very small nozzle while meshing

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Old   May 5, 2022, 02:53
Default Unable to capture very small nozzle while meshing
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SURAJ
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Dear all,

I have a geometry of order 10m and have 12 nozzles (small patches on walls)of diameter 6mm.

When I am performing snappyHexMesh, then nFaces for nozzles is coming "zero". Although I have given very high surfaceRefinement level for nozzles. I am unable to capture it.

Can anybody guide me what should I do to capture nozzles while meshing.
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Old   May 5, 2022, 03:33
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Yann
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Hi Suraj,

In order to help you, we would need more information about your case : screenshots of your geometry and mesh, blockMesh cell size, snappyHexMeshDict...

Regards,
Yann
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Old   May 5, 2022, 07:09
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SURAJ
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Hello Yann,

Thanks for the reply.
I have attached 3 pics. 1st is full geometry. The geometry contains two legs(downLeg and upLeg). The upLeg is shown in pic2. There are 12 small nozzles on upLeg surface. A few are visible from front view as shown in pic3.

Quote:
Quote:
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v2112 |
| \\ / A nd | Website: www.openfoam.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

backgroundMesh
{
xMin -2;
xMax 2;
yMin -5;
yMax 1.8;
zMin -2;
zMax 2;
xCells 100;
yCells 170;
zCells 100;
}

scale 1;

vertices
(
($:backgroundMesh.xMin $:backgroundMesh.yMin $:backgroundMesh.zMin)
($:backgroundMesh.xMax $:backgroundMesh.yMin $:backgroundMesh.zMin)
($:backgroundMesh.xMax $:backgroundMesh.yMax $:backgroundMesh.zMin)
($:backgroundMesh.xMin $:backgroundMesh.yMax $:backgroundMesh.zMin)

($:backgroundMesh.xMin $:backgroundMesh.yMin $:backgroundMesh.zMax)
($:backgroundMesh.xMax $:backgroundMesh.yMin $:backgroundMesh.zMax)
($:backgroundMesh.xMax $:backgroundMesh.yMax $:backgroundMesh.zMax)
($:backgroundMesh.xMin $:backgroundMesh.yMax $:backgroundMesh.zMax)
);

blocks
(
hex (0 1 2 3 4 5 6 7)
(
$:backgroundMesh.xCells
$:backgroundMesh.yCells
$:backgroundMesh.zCells
)
simpleGrading (1 1 1)
);

edges
(
);

boundary
(
);

mergePatchPairs
(
);


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

Quote:
Quote:
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v2112 |
| \\ / A nd | Website: www.openfoam.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object snappyHexMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

// 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
{
mesh1.stl
{
type triSurfaceMesh;
name RH;
regions
{
laddleWalls {name laddleWalls;}
laddleFS {name laddleFS;}
vaccumBC {name vaccumBC;}
vaccumChambWalls {name vaccumChambWalls;}
//inletDown {name inletDown;}
nozzles {name nozzles;}
upLeg {name upLeg;}
downLeg {name downLeg;}
//snorkelOuterWalls {name snorkelOuterWalls;}






}
}

refinementCyl
{
type searchableCylinder;
point1 (-0.7 0 0);
point2 (-0.7 -1.750 0);
radius 0.3;
//type upLegCyl;
//min (-350 0 -350);
//max ( 8.0 0.7 2.5);
}
}


// 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 10000000;

// 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 20000000;

// 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 3;



// 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 "mesh1.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
{
RH
{
level (0 0);

regions
{
nozzles
{
level (8 8);
patchInfo
{
type patch;
}
}
/* inletDown
{
level (5 5);
patchInfo
{
type patch;
}
}
inletUp
{
level (5 5);
patchInfo
{
type patch;
}

} */

vaccumBC
{
level (2 2);
patchInfo
{
type patch;
}

}
laddleFS
{
level (2 2);
patchInfo
{
type patch;
}

}
/*snorkelOuterWalls
{
level (1 1);
patchInfo
{
type wall;
}

} */
vaccumChambWalls
{
level (2 2);
patchInfo
{
type wall;
}

}
laddleWalls
{
level (2 2);
patchInfo
{
type wall;
}

}
downLeg
{
level (2 2);
patchInfo
{
type wall;
}

}
upLeg
{
level (3 3);
patchInfo
{
type wall;
}

}

}
}


}

// Resolve sharp angles
resolveFeatureAngle 90;


// 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
{
refinementCyl
{
mode inside;
levels ((1E15 3));
}
}


// 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 0.3 0);


// 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 0.0002;

//- 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 20;

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

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

//- Detect points on multiple surfaces (only for explicitFeatureSnap)
multiRegionFeatureSnap false;
}



// 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
{
wall
{
nSurfaceLayers 3;
}

moldWalls
{
nSurfaceLayers 3;
}

}

// Expansion factor for layer mesh
expansionRatio 1.3;

// 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.
// See relativeSizes parameter.
finalLayerThickness 0.03;

// 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 0.006;

// 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 1.7.x! (didn't do anything in 1.7.x)
nGrow 0;

// Advanced settings

// When not to extrude surface. 0 is flat surface, 90 is when two faces
// are perpendicular
featureAngle 60;

// At non-patched sides allow mesh to slip if extrusion direction makes
// angle larger than slipFeatureAngle.
slipFeatureAngle 30;

// Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 3;

// 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 1.7.x! 90 degrees corresponds to 130
// in 1.7.x.
minMedialAxisAngle 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
{
#include "meshQualityDict"


// Advanced

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


// Advanced

// Write flags
writeFlags
(
scalarLevels
layerSets
layerFields // write volScalarField for layer coverage
);


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


// ************************************************** *********************** //
Regards,
Suraj
Attached Images
File Type: png pic1_full_image.PNG (88.7 KB, 8 views)
File Type: png pic2_upLeg.PNG (47.0 KB, 9 views)
File Type: png pic3_nozzles.PNG (37.1 KB, 9 views)
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Old   May 6, 2022, 02:35
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Alberto Ceschin
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Run surfaceFeatureExtract and use that output for snappy. In alternative I would refine that area and use topoSet, to select the corresponding faces and use them as inlet for the nozzles. I guess with that low detail you don t care if the nozzles have a cylindrical or square section, as soon as the mass flux matches.
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