Week 8 - BlockMesh Drill down challenge

Mesh specification

1. Number of cells along the x direction (longer dimension) = 200
2. Number of cells along the y direction = 10
3. Use a graded mesh. Grading factor near all walls should be 0.

First the geometry has to be created. So the apprapriate solver is choosed and geotmetry is created in the blockMeshDict c program file found in its system file. I selected icoFoam-cavity in tutorial.so the icofoam folder is copied to run folder in the openfoam directory. then the blockMeshDict file in system file is editedto required Geometry.

Program for geometry:

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  7
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

convertToMeters 0.1;

vertices
(
    (0 0 0) //0
    (0.8 0 0)//1
    (0.8 0.1 0)//2
    (0 0.1 0)//3
    (2 0.1 0)//4
    (2 0 0)//5
    (2 -0.1 0)//6
    (0.8 -0.1 0)//7
    (0 0 0.01)//8
    (0.8 0 0.01)//9
    (0.8 0.1 0.01)//10
    (0 0.1 0.01)//11
    (2 0.1 0.01)//12
    (2 0 0.01)//13
    (2 -0.1 0.01) //14
    (0.8 -0.1 0.01)//15
);

blocks
(
    hex (0 1 2 3 8 9 10 11) (80 10 1) simpleGrading (0.2 0.2 1)
    hex (1 5 4 2 9 13 12 10) (120 10 1) simpleGrading (0.2 0.2 1)
    hex (7 6 5 1 15 14 13 9) (120 10 1) simpleGrading (0.2 0.2 1)
);

edges
(
);

boundary
(
     inlet
    {
        type patch;
        faces
        (
            (0 8 11 3)
        );
    }
    outlet
    {
        type patch;
        faces
        (
            (6 5 13 14)
            (5 4 12 13)
        );
    }
    
    topWalls
    {
        type wall;
        faces
        (
            (11 10 2 3)
            (10 12 4 2)
        );
    }
    botWalls
    {
        type wall;
        faces
        (
            (0 1 9 8)
            (7 6 14 15)
        );
    }
    sideWalls
    {
        type wall;
        faces
        (
             (1 7 9 15)
        );
    }
    frontAndBack
    {
        type empty;
        faces
        (
            (0 3 2 1)
            (1 2 4 5)
            (7 1 5 6)
            (8 9 10 11)
            (9 13 12 10)
            (15 14 13 9)
        );
    }
);

mergePatchPairs
(
);

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

In the above geometry program, mesh grading factor is 0.2. For different mesh grading factor the value in block - hex - simple grading is changed. once the Geometry is done, the initial and boundary condition for velocity and pressure is implied by editing the c program in u and p files in constant. The inlet velocity is assumed to be 1m/s.

program for timestep:

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  7
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application     icoFoam;

startFrom       startTime;

startTime       0;

stopAt          endTime;

endTime         0.5;

deltaT          0.0001;

writeControl    timeStep;

writeInterval   20;

purgeWrite      0;

writeFormat     ascii;

writePrecision  6;

writeCompression off;

timeFormat      general;

timePrecision   6;

runTimeModifiable true;


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

edited velocity program:

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  7
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volVectorField;
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0 0 0);

boundaryField
{
    inlet
    {
        type            fixedValue;
        value           uniform (1 0 0);
    }
    outlet
    {
        type            zeroGradient;
    }


    topWalls
    {
        type            noSlip;
    }
    botWalls
    {
        type            noSlip;
    }
    sideWalls
    {
        type            noSlip;
    }


    frontAndBack
    {
        type            empty;
    }
}

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

edited pressure program:

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  7
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 2 -2 0 0 0 0];

internalField   uniform 0;

boundaryField
{    
    inlet
    {
        type            zeroGradient;
    }
    outlet
    {
        type            fixedValue;
        value           uniform 0;
    }
    topWalls
    {
        type            zeroGradient;
    }

    botWalls
    {
        type            zeroGradient;
    }
    sideWalls
    {
        type            zeroGradient;
    }

    frontAndBack
    {
        type            empty;
    }
}

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

Result:

for mesh Grading factor 0.2:

velocity:

pressure:

velocity graph:

for mesh Grading factor 0.5:

velocity:

pressure:

velocity graph:

for mesh Grading factor 0.8:

velocity:

pressure:

velocity graph:

Thus, the velocity profile at 0.085m is 0.8 m/s. the result from different mesh grading are same. the only difference is the execution time and finess of result. The execution time for mesh grading 0.2,0.5 and 0.8 are 21.64, 20.41 and 19.74 seconds respectively. so the finner the mesh the better the result accuracy and time taken.