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[blockMesh] Blockmesh Spline usage strange simpleGrading behavior

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Old   June 9, 2023, 05:40
Post Blockmesh Spline usage strange simpleGrading behavior
  #1
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Andrea
Join Date: Oct 2022
Posts: 3
Rep Power: 3
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I am trying to make a "smart" mesh for a laminar flame, but I cant get why blockMesh is subdividing the blocks like that (look at the image I linked). I have tried both wiht simplegrading and edgegrading. The problem is on the blocks on the west side, near to the blocks boundaries the mesh goes from fine to course, but this is not specified. The only thing that works is not using any Spline/polyLine. If you have any suggestion/solution I would be happy to hear it.
Thanks in advance.


Code:
/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  10
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

convertToMeters 0.001;

vertices
(
   (0     0                    -15)   // 0

   (8  -0.13962634015954636  -30)   // 1
   (8   0.13962634015954636  -30)   // 2

   (0     0                     15)     // 3

   (8  -0.13962634015954636   0)     // 4
   (8   0.13962634015954636   0)     // 5

   (45  -0.7853981633974483     0)     // 6
   (45   0.7853981633974483     0)     // 7

   (0     0                     90)   // 8

   (8  -0.13962634015954636   75)   // 9
   (8   0.13962634015954636   75)   // 10

   (45  -0.7853981633974483     75)   // 11
   (45   0.7853981633974483     75)   // 12
   (8.5  0.14835298641951802 0) // 13
   (8.5 -0.14835298641951802 75) // 14
   (8.5  0.14835298641951802 75) // 15
   (8.5 -0.14835298641951802 0) // 16
   (0 0 17) // 17
   (8  -0.13962634015954636 2) // 18
   (8  0.13962634015954636 2) // 19
   (8.5 -0.14835298641951802 2) // 20
   (8.5 0.14835298641951802 2) // 21
   (45 -0.7853981633974483 2) // 22
   (45 0.7853981633974483 2) // 23
);

blocks
(
   hex ( 0 1 2 0 3 4 5 3 )   (40 1 40)   edgeGrading (1 1 1 1 1 1 1 1 1 1 1 1) //(0.7 1 0.15) //sw
   hex ( 3 4 5 3 17 18 19 17 )   (40 1 33)   edgeGrading (1 1 1 1 1 1 1 1 1 1 1 1) //(0.7 1 0.7) // cw
   hex ( 17 18 19 17 8 9 10 8 ) (40 1 133) edgeGrading  (1 1 1 1 1 1 1 1 1 1 1 1)//(0.7 1 22) // nw
   hex ( 5 4 16 13 19 18 20 21 )   (1 30 33)   simpleGrading  (1 1 1)//(1 1 0.7) // cc
   hex ( 19 18 20 21 10 9 14 15 ) (1 30 133) simpleGrading  (1 1 1)//(1 1 22) // cn
   hex ( 13 16 6 7 21 20 22 23 ) (1 40 33) simpleGrading  (1 1 1)//(1 3 0.7) // ce
   hex ( 21 20 22 23 15 14 11 12 ) (1 40 133) simpleGrading  (1 1 1)//(1 3 22) // ne

);

boundary
(
    inletFuel
    {
        type patch;
        faces
        (
            (0 1 2 0)
        );
    }

    wallOutside
    {
        type wall;
        faces
        (
            (7 6 23 22)
            (23 22 12 11)
        );
    }

    wallTube
    {
        type wall;
        faces
        (
            (2 1 5 4)
            (5 4 16 13)
        );
    }


    inletN
    {
        type patch;
        faces
        (
            (13 16 6 7)
        );
    }

    outlet
    {
        type patch;
        faces
        (
            (8 9 10 8)
            (10 9 14 15)
            ( 15 14 11 12 )
        );
    }

    axis
    {
        type empty;
        faces
        (
            (0 3 3 0)
            (3 17 17 3)
            (17 8 8 17)
        );
    }

    frontAndBack_pos
    {
        type wedge;
        faces
        (
            (0 2 3 5)
            (3 5 17 19)
            (17 19 8 10)
            (5 13 19 21)
            (19 21 10 15)
            (13 7 21 23)
            (21 23 15 12)
        );
    }

    frontAndBack_neg
    {
        type wedge;
        faces
        (
            (0 1 3 4)
            (3 4 17 18)
            (17 18 8 9)
            (4 16 18 20)
            (18 20 9 14)
            (16 6 20 22)
            (20 22 14 11)
        );
    }
);

edges
(
    BSpline 17 19 ((0.2 0.003490658503988659 17) (1 0.017453292519943295 16.7) (7 0.12217304763960307 2.3) (7.8 0.1361356816555577 2))
    BSpline 17 18 ((0.2 -0.003490658503988659 17) (1 -0.017453292519943295 16.7) (7 -0.12217304763960307 2.3) (7.8 -0.1361356816555577 2))
    BSpline 3 4 ((0.2 -0.003490658503988659 15) (1 -0.017453292519943295 14.7) (7 -0.12217304763960307 0.3) (7.8 -0.1361356816555577 0))
    BSpline 3 5 ((0.2 0.003490658503988659 15) (1 0.017453292519943295 14.7) (7 0.12217304763960307 0.3) (7.8 0.1361356816555577 0))
    BSpline 0 1 ((0.2 -0.003490658503988659 -15) (1 -0.017453292519943295 -15.3) (7 -0.12217304763960307 -29.7) (7.8 -0.1361356816555577 -30))
    BSpline 0 2 ((0.2 0.003490658503988659 -15) (1 0.017453292519943295 -15.3) (7 0.12217304763960307 -29.7) (7.8 0.1361356816555577 -30))
    BSpline 8 9 ((0.2 -0.003490658503988659 90) (1 -0.017453292519943295 89.7) (7 -0.12217304763960307 75.3) (7.8 -0.1361356816555577 75))
    BSpline 8 10 ((0.2 0.003490658503988659 90) (1 0.017453292519943295 89.7) (7 0.12217304763960307 75.3) (7.8 0.1361356816555577 75))
);
// ************************************************************************* //
Attached Images
File Type: jpg badMesh.jpg (51.5 KB, 36 views)

Last edited by exnihilo; June 9, 2023 at 05:48. Reason: further explainations
exnihilo is offline   Reply With Quote

Old   June 10, 2023, 04:32
Default
  #2
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shinji nakagawa
Join Date: Mar 2009
Location: Japan
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Rep Power: 18
snak is on a distinguished road
Hi exnihilo,

Thank you for sharing interesting problem.

It looks like that positions given in spline edges prevents grading.

I cannot suggest a direct solution unfortunately.

To avoid the problem, we may use geometry and projection in blockMesh dict. With this method grading instruction works. I modified your dict as follows. Curves is obtained from spheres created in geometry sub-dict. Your can use arbitrary shape (stl files and others) instead of sphere.

https://develop.openfoam.com/Develop.../blockMeshDict

https://www.openfoam.com/documentati...-geometry.html


Code:
/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  10
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //


// OpenFOAM v2212

 
scale 0.001;

// Geometric parameters
outerRadius 8;

geometry
{
    sphere0
    {
        type    sphere;
        origin  (0 0 -30);
        radius  $outerRadius;
    }
    sphere1
    {
        type    sphere;
        origin  (0 0 0);
        radius  $outerRadius;
    }
    sphere2
    {
        type    sphere;
        origin  (0 0 2);
        radius  $outerRadius;
    }
    sphere3
    {
        type    sphere;
        origin  (0 0 75);
        radius  $outerRadius;
    }
}

vertices
(
   (0     0                  -22) // -15)   // 0
   (8  -0.13962634015954636  -30)   // 1
   (8   0.13962634015954636  -30)   // 2
   //project (0 0 -15) (sphere)  // 0
   //project (8  -0.13962634015954636 -30) (sphere)  // 1
   //project (8   0.13962634015954636  -30) (sphere)  // 2

   (0     0                   8) //  15)     // 3
   (8  -0.13962634015954636   0)     // 4
   (8   0.13962634015954636   0)     // 5

   (45  -0.7853981633974483     0)     // 6
   (45   0.7853981633974483     0)     // 7

   (0     0                   83) //  90)   // 8

   (8  -0.13962634015954636   75)   // 9
   (8   0.13962634015954636   75)   // 10

   (45  -0.7853981633974483     75)   // 11
   (45   0.7853981633974483     75)   // 12
   (8.5  0.14835298641951802 0) // 13
   (8.5 -0.14835298641951802 75) // 14
   (8.5  0.14835298641951802 75) // 15
   (8.5 -0.14835298641951802 0) // 16

   (0 0 10) //17) // 17
   (8  -0.13962634015954636 2) // 18
   (8  0.13962634015954636 2) // 19

   (8.5 -0.14835298641951802 2) // 20
   (8.5 0.14835298641951802 2) // 21
   (45 -0.7853981633974483 2) // 22
   (45 0.7853981633974483 2) // 23
);

blocks
(
   hex ( 0 1 2 0         3 4 5 3 ) (40 1  40) simpleGrading (0.25 1 1) // block 0  //(0.7 1 0.15) //sw
   hex ( 3 4 5 3     17 18 19 17 ) (40 1  33) simpleGrading (0.25 1 1) //block 1 //(0.7 1 0.7) // cw
   hex ( 17 18 19 17    8 9 10 8 ) (40 1 133) simpleGrading  (0.25 1 1) // block 2 //(0.7 1 22) // nw
   hex ( 5 4 16 13   19 18 20 21 ) (1 30  33) simpleGrading  (1 1 1)//(1 1 0.7) // cc
   hex ( 19 18 20 21  10 9 14 15 ) (1 30 133) simpleGrading  (1 1 1)//(1 1 22) // cn
   hex ( 13 16 6 7   21 20 22 23 ) (1 40  33) simpleGrading  (1 1 1)//(1 3 0.7) // ce
   hex ( 21 20 22 23 15 14 11 12 ) (1 40 133) simpleGrading  (1 1 1)//(1 3 22) // ne
);

boundary
(
    inletFuel
    {
        type patch;
        faces
        (
            (0 1 2 0)
        );
    }

    wallOutside
    {
        type wall;
        faces
        (
            (7 6 23 22)
            (23 22 12 11)
        );
    }

    wallTube
    {
        type wall;
        faces
        (
            (2 1 5 4)
            (5 4 16 13)
        );
    }

    inletN
    {
        type patch;
        faces
        (
            (13 16 6 7)
        );
    }

    outlet
    {
        type patch;
        faces
        (
            (8 9 10 8)
            (10 9 14 15)
            ( 15 14 11 12 )
        );
    }

    axis
    {
        type empty;
        faces
        (
            (0 3 3 0)
            (3 17 17 3)
            (17 8 8 17)
        );
    }

    frontAndBack_pos
    {
        type wedge;
        faces
        (
            (0 2 3 5)
            (3 5 17 19)
            (17 19 8 10)
            (5 13 19 21)
            (19 21 10 15)
            (13 7 21 23)
            (21 23 15 12)
        );
    }

    frontAndBack_neg
    {
        type wedge;
        faces
        (
            (0 1 3 4)
            (3 4 17 18)
            (17 18 8 9)
            (4 16 18 20)
            (18 20 9 14)
            (16 6 20 22)
            (20 22 14 11)
        );
    }
);

edges
(
    //BSpline 17 19 ((0.2 0.003490658503988659 17) (1 0.017453292519943295 16.7) (7 0.12217304763960307 2.3) (7.8 0.1361356816555577 2))
    //BSpline 17 18 ((0.2 -0.003490658503988659 17) (1 -0.017453292519943295 16.7) (7 -0.12217304763960307 2.3) (7.8 -0.1361356816555577 2))

    project 17 19 (sphere2) // block 1-0 block 2-
    project 17 18 (sphere2) // block 1-1 block 2-


    //BSpline 3 4 ((0.2 -0.003490658503988659 15) (1 -0.017453292519943295 14.7) (7 -0.12217304763960307 0.3) (7.8 -0.1361356816555577 0))
    //BSpline 3 5 ((0.2 0.003490658503988659 15) (1 0.017453292519943295 14.7) (7 0.12217304763960307 0.3) (7.8 0.1361356816555577 0))

    project 3 4 (sphere1) // block 0-3
    project 3 5 (sphere1) // block 0-2


/*
    // BSpline
    simpleSpline 0 1 
    (
        (0.2 -0.003490658503988659 -15)
        (1   -0.017453292519943295 -15.3)
        (7   -0.12217304763960307  -29.7)
        (7.8 -0.1361356816555577   -30)
    )

    //BSpline
    simpleSpline 0 2 ((0.2 0.003490658503988659 -15) (1 0.017453292519943295 -15.3) (7 0.12217304763960307 -29.7) (7.8 0.1361356816555577 -30))
*/

    project 0 1 (sphere0) // block 0-0
    project 0 2 (sphere0) // block 0-1


    //BSpline 8 9 ((0.2 -0.003490658503988659 90) (1 -0.017453292519943295 89.7) (7 -0.12217304763960307 75.3) (7.8 -0.1361356816555577 75))
    //BSpline 8 10 ((0.2 0.003490658503988659 90) (1 0.017453292519943295 89.7) (7 0.12217304763960307 75.3) (7.8 0.1361356816555577 75))

    project 8 9 (sphere3) // block 2-0
    project 8 10 (sphere3) // block 2-1
);

    // https://develop.openfoam.com/Development/openfoam/-/blob/master/tutorials/mesh/blockMesh/sphere7ProjectedEdges/system/blockMeshDict
faces
(
    project (0 4) sphere0 // block 1: z-min
    project (0 5) sphere1 // block 1: z-max
    project (1 4) sphere1 // block 2: z-min
    project (1 5) sphere2 // block 2: z-max
    project (2 4) sphere2 // block ?: z-min
    project (2 5) sphere3 // block ?: z-max
);

// ************************************************************************* //
Attached Images
File Type: jpg mesh.jpg (125.6 KB, 28 views)
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Old   June 10, 2023, 04:42
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  #3
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Andrea
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Thank you very much! I thought spline was a good instrument since I could have made the flame on a super coarse mesh with a 1/2 step reaction mechanism and then I could have easily fitted the flame front on the spline. This would result in a super fine mesh where needed, but I think I can do something similar with a sphere, just fitting the sphere or with a generated .stl file. Thank you very much again for the suggestions, I will probably add this to the issues on openfoam site.
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