[MohdShaeq]

Hello everyone,

I am trying to mesh a hydrogen engine combustion chamber and some of its other parts in order to study its carburation characteristics. For that I have used snappyHexMesh, which however fails to properly mesh some critical parts such as Needle and Nozzle, among others, the images of which are attached herewith. The InletPatch is completely missing. I think is a snapping problem and in order to rectify this, I have increased the number of snapping relaxation iterations, nRelaxIter, from 5 to 15, which has improved the results. But it reaches a limit at 30. This, however, has no effect on the InletPatch.

The blockMeshDict is as follows:-

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1912                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

scale   1;

xMin -0.087;
xMax  0.072;
yMin -0.071;
yMax  0.080;
zMin -0.161;
zMax  0.049;
vertices // Eckpunkte Koordinaten auf xyz - Achsen des Hexaedars
(
    ($xMin $yMin $zMin)
    ($xMax $yMin $zMin)
    ($xMax $yMax $zMin)
    ($xMin $yMax $zMin)
    ($xMin $yMin $zMax)
    ($xMax $yMin $zMax)
    ($xMax $yMax $zMax)
    ($xMin $yMax $zMax)
);

blocks
(
    hex (0 1 2 3 4 5 6 7) (20 20 20) simpleGrading (1 1 1)
);

edges
(
);

patches
(
    wall Walls
    (
        (2 6 5 1)
        (0 4 7 3)
        (0 1 5 4)
        (4 5 6 7)
        (7 6 2 3)
        (3 2 1 0)
    )
);

mergePatchPairs
(
);

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

The snappyHexMeshDict is as follows:-

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1912                                 |
|   \\  /    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       false;

// 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
{
	Geometry // STL filename
	{
		type triSurfaceMesh;
		file "Geometry.stl";

		regions
		{
			IntakeManifold {name IntakeManifold;}
			ExhaustManifold {name ExhaustManifold;}
			Nozzle {name Nozzle;}
			InletPatch {name InletPatch;}
			SprayChamber {name SprayChamber;}
			InjectorFluidchamber {name InjectorFluidchamber;}
			InjectorFluidvolume {name InjectorFluidvolume;}
			Needle {name Needle;}
		}
	}
};

// Settings for the castellatedMesh generation.	
castellatedMeshControls		//sub-dictionary of controls for castellated mesh.
{ 
	// 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; //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 30000000; //1000000
	
	// 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; //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 1;


	// 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 "Geometry.eMesh";
		level 4; //4; //5; //6
		}
	);

	// 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
	{
		Geometry
		{
			// Surface - wise min and max refinement level
			level (1 1);
			regions
			{
				IntakeManifold {level (1 1); patchInfo {type wall;}}
				ExhaustManifold {level (1 1); patchInfo {type wall;}}
				Nozzle {level (4 4); patchInfo {type wall;}}
				InletPatch {level (4 4); patchInfo {type patch;}}
				SprayChamber {level (2 2); patchInfo {type wall;}}
				InjectorFluidchamber {level (4 4); patchInfo {type wall;}}
				InjectorFluidvolume {level (4 4); patchInfo {type wall;}}
				Needle {level (4 4); patchInfo {type wall;}}
			}
		}
	}

	// 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
	{
		Geometry
		{
			mode distance;
			levels ((1.0 0) (2.0 0));
			regions
			{
				Nozzle
				{
				mode inside;
				levels ((1E15 4));
				}

				InletPatch
				{
				mode inside;
				levels ((1E15 4));
				}

				SprayChamber
				{
				mode inside;
				levels ((1E15 2));
				}

				InjectorFluidchamber
				{
				mode inside;
				levels ((1E15 4));
				}

				InjectorFluidvolume
				{
				mode inside;
				levels ((1E15 4));
				}

				Needle
				{
				mode inside;
				levels ((1E15 4));
				}
			}
		}
	}
		
	// 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.

		locationsInMesh
		(
			((0 0.046 0.005) IntakeManifold) // Inside Point
			((0 0.025 -0.15) ExhaustManifold)
			((0 0.0027 0) Nozzle)
			((0 -0.0016 0.00698) InletPatch)
			((0 0 -0.06) SprayChamber)
			((0 0 -0.01) InjectorFluidchamber)
			((0 -0.003 0.006) InjectorFluidvolume)
		    ((0 0 0) Needle)
		);
	// 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;

	//- Number of iterations for internal smoothing to reduce non-orthogonality
	//  at the face of refinement (effectively making the faces non-planar).
	//  Default value is zero.
	nSmoothInternal $nSmoothPatch;

	//- Relative distance for points to be attracted by surface feature point
    //  or edge. True distance is this factor times local
    //  maximum edge length. This factor multiplied by local cell-edge length
	//  specifies region along the surface within which the points are attracted by the surface.
	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.  If the mesh does not conform
	//  the geometry and all the iterations are spend, user may try to increase the number of iterations.
	nRelaxIter 15;

	// Feature snapping

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

		// - Detect ( geometric only ) features by sampling the surface
		// ( default = false ). When turned on, the snappyHexMesh does not read eMesh file
		//   and defines the sharp edges itself. Implicit algorithm behaves
		//   correctly on simple meshes without sharp corners and baffles.
		implicitFeatureSnap false ;

		// - Use castellatedMeshControls :: features ( default = true )
		//   Snap mesh onto the feature lines defined in eMesh file.
		explicitFeatureSnap true ;

		// - Detect points on multiple surfaces ( only for explicitFeatureSnap )
		//   When using explicitFeatureSnap and this switch is on, features between
		//   multiple surfaces will be captured. This is useful for multi-region meshing
		//   where the internal mesh must conform the region geometrical boundaries. Default = false.
		multiRegionFeatureSnap true ;
 }
 
 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
    {
	   SprayChamber
       {
		   nSurfaceLayers 3;
	   }

	   Nozzle
       {
		   nSurfaceLayers 1;
	   }

	   InjectorFluidchamber
       {
		   nSurfaceLayers 3;
	   }

	   InjectorFluidvolume
       {
		   nSurfaceLayers 3;
	   }

	   Needle
       {
		   nSurfaceLayers 3;
	   }
    }

    // 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.
    // See relativeSizes parameter.
    finalLayerThickness 0.3;

    // 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;

    // 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"

	maxNonOrtho 65;
    maxBoundarySkewness 20;
    maxInternalSkewness 4;
    maxConcave 80;
    minVol 1e-13;
    minTetQuality 1e-13;
    minArea -1;
    minTwist 0.05;
    minDeterminant 0.001;
    minFaceWeight 0.05;
    minVolRatio 0.01;
    minTriangleTwist -1;

	/*
	// Optional : some meshing phases allow usage of relaxed rules.
    // See e.g. addLayersControls::nRelaxedIter.
    relaxed
    {
        //- Maximum non-orthogonality allowed. Set to 180 to disable.
        maxNonOrtho 75;
    }

    // Advanced

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

    // Advanced
    nSmoothScale 4;
    errorReduction 0.75;

    relaxed
    {
        maxNonOrtho 55;
    }

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


// Write flags
writeFlags
(
    scalarLevels	// write volScalarField with cellLevel for postprocessing
    layerSets		// write cellSets, faceSets of faces in layer
    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;


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

Kindly guide me on how can I completely remove this problem and obtain a high quality mesh. I would be highly obliged to you.

Kind regards,
Shaeq

[AtoHM]

Why do you create a new post for this?
Avoiding highly skewed faces and generating a high quality 3D-Mesh

[MohdShaeq]

How do I delete this post on the same topic?