## Edge Mesh Creation - Stator Region

Edge meshing is important part of meshing using snappyHexMesh. Edge meshing feature helps a lot to eliminate problems with catching sharp edges of objects or in determining intersections between boundaries. Utility surfaceFeatureExtract can extract sharp edges from .STL surfaces. This utility reads settings from its dictionary file surfaceFeatureExtractDict located in system subdirectory.

Let us view content of an example surfaceFeatureExtractDict extracting sharp edges from file t-housing.stl:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.2.2                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
version     2.0;
format      ascii;
class       dictionary;
object      surfaceFeatureExtractDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

t-housing.stl
{
extractionMethod    extractFromSurface;

extractFromSurfaceCoeffs
{
includedAngle   100;
}

writeObj                yes;
}

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

It extracts edge features and saves it to a new file t-housing.eMesh located in the constant/triSurface subdirectory. Parameter includedAngle specifies an angle in degrees. Edges having lower angle between its faces are written down. Parameter writeObj set to yes means the output will also be written in the .obj format to the constant/extendedFeatureEdgeMesh subdirectory. This format can be viewed directly in paraview. To run the utility, use following command:
surfaceFeatureExtract

Another case is when two surfaces ( t-housing.stl and interface-t1.stl) have their common intersection to be caught. Utility surfaceBooleanFeatures can extract the intersection between two .stl surfaces.

surfaceBooleanFeatures intersection constant/triSurface/t-housing.stl constant/
triSurface/interface-t1.stl

Several unnecessary .obj files were created in the case directory and these can be removed.

rm -rf *.obj
The resulting edge features can be viewed using paraview.

paraview

Figure: Feature edges of turbine housing (black) and intersections (red).