[Alejandro_Dominguez]

Hello, first of all this is my first question in the forum so I apologise for any mistake I can make.
I am trying to create a 3D C-grid with blockMesh to use it as background mesh in snappyHexMesh, and I have almost succeeded except for a problem with face matching. To create it, I have divided the domain in 2 quarters of cylinders and 1 prism, but the problem is that blockMesh sets as defaultFaces the face between the prism and the two quarters and this is a face I expected that blockMesh would ignore. When I tried to use mergePatchPairs as an alternative I got an error message about no cell neighbours faces.
I attatch the blockMeshDict and an Image of the C-grid side with the problematic face outlined in red.

Does anyone know how to remove that defaultFace or how to correct my blockMeshDict so this problem does not appear?

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1812                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

convertToMeters 1;

vertices
(
    (74 844.8 0)//0
	(-770.8 0 0)//1
	(74 -844.8 0)//2
	(74 844.8 30)//3
	(-770.8 0 30)//4
	(74 -844.8 30)//5
	(74 0 0)//6
	(74 0 30)//7
	(844.8 -844.8 0)//8
	(844.8 844.8 0)//9
	(844.8 844.8 30)//10
	(844.8 -844.8 30)//11

	
);

blocks
(
    hex (1 2 6 6 4 5 7 7) (20 20 2) simpleGrading (1 1 1) //cuarto de cilindro
	hex (0 1 6 6 3 4 7 7) (20 20 2) simpleGrading (1 1 1) //cuarto de cilindro
	hex (0 2 8 9 3 5 11 10) (30 15 2) simpleGrading (1 1 1) //cubo (30 celdas en y 15 en x )
);

edges
(
	arc 1 2 (-523.3638087 -597.3638087 0)
	arc 0 1 (-523.3638087 597.3638087 0)
	arc 4 5 (-523.3638087 -597.3638087 30)
	arc 3 4 (-523.3638087 597.3638087 30)
);

boundary
(
    inlet
    {
        type patch;
        faces
        (
            (5 4 1 2)
			(4 3 0 1)
        );
    }
    outlet
    {
        type patch;
        faces
        (
            (8 9 10 11)
        );
    }
    
    frontAndBack
    {
        type symmetry;
        faces
        (
			(3 4 7 7)
			(4 5 7 7)
			(5 11 10 3)
			(2 1 6 6)
			(1 0 6 6)
			(0 9 8 2)
        );
    }
	
	topAndBottom
    {
        type wall;
        faces
        (
            (3 10 9 0)
			(5 2 8 11)
        );
    }
	
);

mergePatchPairs
(
	//(  ) merge patch pair 0 
);

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

blockMeshDict.txt

Thank you!!

[aow]

I would try splitting the third hex you’re trying to create into two separate hexes along the line y = 0. As far as I know, you can’t create a hex that has a face connected to 2 faces of 2 different hexes.

So you would need to add an additional pair of vertices...

(844.8 0 0) //12
(844.8 0 30) //13

split the third hex into...
hex(0 6 12 9 3 7 13 10)
hex(6 2 8 12 7 5 11 13)

Of course you would also need to edit the boundaries appropriately too. Note I have not actually run your blockMeshDict to check my edits (I’m using my phone to write to you), but I believe this approach is the correct one to take. Good luck!