Week 8 - BlockMesh Drill down challenge

AIM: Simulating the flow through backward facing step using icoFOAM solver.

PROCEDURE:  

• icoFOAM solves the incompressible laminar navier stokes equations using PISO algorithm.
• Path to find solver

      tutorials -> incompressible -> icoFOAM

Mesh generation

• To create the BFS,we have to edit the blockmeshdict file available in the system directory.

Grading factor 0.2

/*--------------------------------*- 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 1;

vertices
(
    (0 0 0)        //ver0
    (0.08 0 0)     //ver1
    (0.08 0.005 0) //ver2
    (0 0.005 0)    //ver3
    (0.08 0.01 0)  //ver4
    (0 0.01 0)     //ver5
    (0.2 0.01 0)   //ver6
    (0.2 0.005 0)  //ver7
    (0.2 0 0)      //ver8
    (0.2 -0.01 0)  //ver9
    (0.08 -0.01 0) //ver10
    (0 0 0.001)    //ver11
    (0.08 0 0.001) //ver12
    (0.08 0.005 0.001)  //ver13
    (0 0.005 0.001)   //ver14
    (0.08 0.01 0.001) // ver15
    (0 0.01 0.001)    //ver16
    (0.2 0.01 0.001)  //ver17
    (0.2 0.005 0.001) //ver18
    (0.2 0 0.001)     //ver19
    (0.2 -0.01 0.001) //ver20
    (0.08 -0.01 0.001)//ver21

);

blocks
(
    hex (0 1 2 3 11 12 13 14) (200 10 1) simpleGrading (1 5 1)
    hex (3 2 4 5 14 13 15 16) (200 10 1) simpleGrading (1 0.2 1)
    hex (2 7 6 4 13 18 17 15) (200 10 1) simpleGrading (2 0.2 1)
    hex (1 8 7 2 12 19 18 13) (200 10 1) simpleGrading (5 5 1)
    hex (10 9 8 1 21 20 19 12) (200 10 1) simpleGrading (5 5 1)
);

edges
(
);

boundary
(
    inletWall
    {
        type patch;
        faces
        (
            (0 11 14 3)
            (3 14 16 5)
        );
    }
    outletWalls
    {
        type patch;
        faces
        (
            (9 8 19 20)
            (8 7 18 19)
            (7 6 17 18)
        );
    }
    frontAndBack
    {
        type empty;
        faces
        (
            (0 3 2 1)
            (3 5 4 2)
            (2 4 6 7)
            (1 2 7 8)
            (10 1 8 9)
            (11 12 13 14)
            (14 13 15 16)
            (13 18 17 15)
            (12 19 18 13)
            (21 20 19 12)
        );
    }
    Noslipwalls
    {
        type wall;
        faces
        (
        (5 16 15 4)
        (4 15 17 6)
        (0 1 12 11)
        (10 9 20 21)
        (1 10 21 12)

        );
     
      }
      
);

mergePatchPairs
(
);

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

Mesh with grading factor 0.2

Grading factor 0.5

blocks
(
    hex (0 1 2 3 11 12 13 14) (200 10 1) simpleGrading (1 2 1)
    hex (3 2 4 5 14 13 15 16) (200 10 1) simpleGrading (1 0.5 1)
    hex (2 7 6 4 13 18 17 15) (200 10 1) simpleGrading (2 0.5 1)
    hex (1 8 7 2 12 19 18 13) (200 10 1) simpleGrading (2 2 1)
    hex (10 9 8 1 21 20 19 12) (200 10 1) simpleGrading (2 2 1)
);

Mesh with 0.5 rading factor:

Grading factor 0.8

blocks
(
    hex (0 1 2 3 11 12 13 14) (200 10 1) simpleGrading (1 1.25 1)
    hex (3 2 4 5 14 13 15 16) (200 10 1) simpleGrading (1 0.8 1)
    hex (2 7 6 4 13 18 17 15) (200 10 1) simpleGrading (1.25 0.8 1)
    hex (1 8 7 2 12 19 18 13) (200 10 1) simpleGrading (1.25 1.25 1)
    hex (10 9 8 1 21 20 19 12) (200 10 1) simpleGrading (1.25 1.25 1)
);

 Mesh with 0.8 grading factor

Boundary conditions:

The boundary conditions can be given by editing the pressure and velocity script files available 0 folder.

Pressure script file:

/*--------------------------------*- 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
{
    inletWall
    {
        type            zeroGradient;
    }

    outletWalls
    {
        type            fixedValue;
        value           uniform 0;
    }

    frontAndBack
    {
        type            empty;
    }
    Noslipwalls
    {
        type            zeroGradient;   
    }        
}

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

Velocity script:

/*--------------------------------*- 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
{
    inletWall
    {
        type            fixedValue;
        value           uniform (3 0 0);
    }

    outletWalls
    {
        type            zeroGradient;
    }

    frontAndBack
    {
        type            empty;
    }
    Noslipwalls
    {
        type            noSlip;
        value           uniform (0 0 0);
    }
}

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

control script:

/*--------------------------------*- 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         0.02;

deltaT          1e-5;

writeControl    timeStep;

writeInterval   15;

purgeWrite      0;

writeFormat     ascii;

writePrecision  6;

writeCompression off;

timeFormat      general;

timePrecision   6;

runTimeModifiable true;


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

Post processing:

Velocity contours

Grading factor 0.2

Grading factor 0.5

Grading factors 0.8

Results:

0.2 grading factor

0.5 grading factor

0.8 grading factor

Conclusion:

As grading factor increases the velocity also increases but very minutely as the change is negligible.