[mcfdma]

Hello. Can anyone guide me on how to use snappyHexMesh for a 3D model going from Fig3 to Fig6?
Fig3.JPG
Fig6.JPG

To avoid complexity and get a good understanding, I have started off simple.

1. Using Solidworks, I made a cylinder (with thickness), extruded it and made a shell at the outlet end to allow fluid to enter. I also created a second unattached body (extractor ring) further downstream using reference plane geometry as shown in the figure. I saved it as a single stl file (ASCII and refine). The inlet side is closed as I assume it will help me make that surface as patch.
pip4.PNG
pip4_2.PNG

2. Following WolfDynamics and few other youtube videos, I use:
a. surfaceAutoPatch geometry/combined.stl output.stl 150 to get 9 patches (0 - 8)
patch0 - outer cylinder wall
patch1 - exit of cylinder (ring)
patch2 - inlet: back end of outer cylinder (fully covered)
patch3 - inner cylinder wall
patch4 - inlet: back end of inner cylinder
patch 5 - back extractor ring
patch6 - front extractor ring (facing the cylinder)
patch 7 -outer ring, patch8 - inner ring.

b. I am able to get view the two parts and patches on paraview using output.stl
own.JPG
c. The issue comes when I do snappyHexMesh -overwrite where I am getting the issue.

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.x                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     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
{
    output.stl
    {
        type triSurfaceMesh;
        name mixing_elbow;
         

// First entry in named region in the STL file
// Second entry is user-defined patch name
        regions
        {
            patch0 {name emitter;}
            patch1 {name emitter;}
            patch2 {name emitter;}
            patch3 {name emitter;}
            patch4 {name inlet;}
            patch5 {name extractor;}
            patch6 {name extractor;}
            patch7 {name extractor;}
            patch8 {name extractor;}
        }
    }

};

// Settings for the castellatedMesh generation.
castellatedMeshControls
{
    // Refinement parameters
    maxLocalCells 			100000;
    maxGlobalCells 			20000000;
    minRefinementCells 			10;
    maxLoadUnbalance 			0.10;
    nCellsBetweenLevels 		2;
    allowFreeStandingZoneFaces 		true;
    resolveFeatureAngle 		30;		
    planarAngle 			30;


    // Explicit feature edge refinement
    features
    (
        { file "pip4.eMesh"; level 0; }
    );

    // Surface based refinement
    refinementSurfaces
    {
        mixing_elbow
        {
            // Global surface-wise min and max refinement level
            level (0 0);

            // Local surface-wise min and max refinement level
			// You will need to use the name given in the STL file
            regions
			{
            	"(patch0|patch1|patch2|patch3)"	//emitter
                { level (1 1); patchInfo { type wall; } }

            	patch4				//inlet 
                { level (1 1); patchInfo { type patch; } }

            	"(patch5|patch6|patch7|patch8)"	//pipe
                { level (1 1); patchInfo { type wall; } }
			}
        }
    }


    // Region-wise refinement
    refinementRegions
    {
        mixing_elbow
        {
            mode distance;		//distance, inside, outside
            levels ((1e-4 0));
        }
    }


    // Mesh selection
    locationInMesh (0 18 20); 

}

// Settings for the snapping.
snapControls
{
    nSmoothPatch 	3;
    tolerance 		2.0;
    nSolveIter 		100;
    nRelaxIter 		5;

    // Feature snapping
	nFeatureSnapIter 10;

	implicitFeatureSnap false;
	explicitFeatureSnap true;

	// Detect features between multiple surfaces
	// (only for explicitFeatureSnap, default = false)
	multiRegionFeatureSnap false;
}

// Settings for the layer addition.
addLayersControls
{
    relativeSizes 		true;
	expansionRatio 		1.2;
	finalLayerThickness 	0.5;
	minThickness 		0.01;

    layers
    {
        pipe { nSurfaceLayers 5; }
    }


    // Advanced settings
    featureAngle 			30;	
    slipFeatureAngle 			30;

    nGrow 				0;

    nLayerIter 				50;
    nRelaxedIter 			20;
    nRelaxIter 				5;

    nSmoothSurfaceNormals 		1;
    nSmoothNormals 			3;
    nSmoothThickness 			10;
    maxFaceThicknessRatio 		0.5;
    maxThicknessToMedialRatio 		0.3;

    minMedialAxisAngle 			90;
    minMedianAxisAngle 			90;
    nMedialAxisIter           		10;

    nBufferCellsNoExtrude 		0;
    additionalReporting 		false;
}

// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
    #include "meshQualityDict"

    relaxed
    {
        maxNonOrtho 75;
    }

    //minFlatness 0.5;

    // Advanced
    nSmoothScale 4;
    errorReduction 0.75;
}

// Advanced
debug 0;

//// Debug flags
debugFlags
(
    //mesh            // write intermediate meshes
    //intersections   // write current mesh intersections as .obj files
    //featureSeeds    // write information about explicit feature edge 

refinement
    //attraction      // write attraction as .obj files
    //layerInfo       // write information about layers
);

//// 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;

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

For some reason, I am getting the mesh cylinder but the extractor ring disappears? Could this be due to locationInMesh where I just mentioned the cylinder?

Any help is appreciated. Thank you

[mcfdma]

Fig 4 shows the extractor ring which isn't present in Fig 3 or Fig6.
Fig3-5.png

[Marpole]

You may need to mesh them separately, i.e making two meshes: one is for the cylinder and one for the ring.