BlockMesh Drill Down Challenge
Objective : Using the icoFOAM solver to simulate the flow through a backward facing step. Creating multiple meshes and comparing results.
Theory :
A backward facing step is generated using OpenFOAM as per the given dimesnsional specifications.
Mesh Specification :
1. Number of cells in x-direction = 200
2. Number of cells in y-direction = 10
3. Grading near the walls = 0.2
Solution steps :
1. Open the tutorials folder by navigating through command prompt. Open folder named incompressible inside it and then navigate to icoFoam folder. Copy the folder named inside icoFoam folder.
2. Paste a copy of cavity folder inside Run folder.
3. Open the blockmesh file in system folder and edit it.
4. Open the \'p\' and \'u\' files and apply boundary conditions for pressure and velocity.
5. Open the ControlDict file and edit time steps according to requirement.
6. Visualise the results using Paraview post procesing tools.
1.For Grading factor of 0.2:
a. BlockMesh 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 dictionary;
object blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
convertToMeters 1;
vertices
(
(0 0 0) // Ver 0
(0.08 0 0) // Ver 1
(0.08 0.005 0) // Ver 2
(0 0.005 0) // Ver 3
(0.08 0.01 0) // Ver 4
(0 0.01 0) // Ver 5
(0.2 0.01 0) // Ver 6
(0.2 0.005 0) // Ver 7
(0.2 0 0) // Ver 8
(0.2 -0.01 0) // Ver 9
(0.08 -0.01 0) // Ver 10
(0 0 0.001) // Ver 11
(0.08 0 0.001) // Ver 12
(0.08 0.005 0.001) // Ver 13
(0 0.005 0.001) // Ver 14
(0.08 0.01 0.001) // Ver 15
(0 0.01 0.001) // Ver 16
(0.2 0.01 0.001) // Ver 17
(0.2 0.005 0.001) // Ver 18
(0.2 0 0.001) // Ver 19
(0.2 -0.01 0.001) // Ver 20
(0.08 -0.01 0.001) // Ver 21
);
blocks
(
hex (0 1 2 3 11 12 13 14) (130 10 1) simpleGrading (1 5 1) //Block 1
hex (3 2 4 5 14 13 15 16) (130 10 1) simpleGrading (1 0.2 1) //Block 2
hex (2 7 6 4 13 18 17 15) (200 10 1) simpleGrading (5 0.2 1) //Block 3
hex (1 8 7 2 12 19 18 13) (200 10 1) simpleGrading (5 5 1) //Block 4
hex (10 9 8 1 21 20 19 12) (200 10 1) simpleGrading (5 5 1) //Block 5
);
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
(
);
// ************************************************************************* //b. ControlDict 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 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;
// ************************************************************************* //c. Pressure Boundary Conditions 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 1;
boundaryField
{
inletWall
{
type zeroGradient;
}
outletWalls
{
type fixedValue;
value uniform 0;
}
frontAndBack
{
type empty;
}
Noslipwalls
{
type zeroGradient;
}
}
// ************************************************************************* //d. Velocity Boundary Conditions 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 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);
}
}
// ************************************************************************* //
PLOTS:
i. Pressure contour plot
ii. Velocity contour plot
iii. Line plot a distance of 0.085 from x
2. For Grading Factor of 0.5
Only BlockMesh is updated while remaining other conditions remain same.
/*--------------------------------*- 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) // Ver 0
(0.08 0 0) // Ver 1
(0.08 0.005 0) // Ver 2
(0 0.005 0) // Ver 3
(0.08 0.01 0) // Ver 4
(0 0.01 0) // Ver 5
(0.2 0.01 0) // Ver 6
(0.2 0.005 0) // Ver 7
(0.2 0 0) // Ver 8
(0.2 -0.01 0) // Ver 9
(0.08 -0.01 0) // Ver 10
(0 0 0.001) // Ver 11
(0.08 0 0.001) // Ver 12
(0.08 0.005 0.001) // Ver 13
(0 0.005 0.001) // Ver 14
(0.08 0.01 0.001) // Ver 15
(0 0.01 0.001) // Ver 16
(0.2 0.01 0.001) // Ver 17
(0.2 0.005 0.001) // Ver 18
(0.2 0 0.001) // Ver 19
(0.2 -0.01 0.001) // Ver 20
(0.08 -0.01 0.001) // Ver 21
);
blocks
(
hex (0 1 2 3 11 12 13 14) (130 10 1) simpleGrading (1 2 1) //Block 1
hex (3 2 4 5 14 13 15 16) (130 10 1) simpleGrading (1 0.5 1) //Block 2
hex (2 7 6 4 13 18 17 15) (200 10 1) simpleGrading (5 0.5 1) //Block 3
hex (1 8 7 2 12 19 18 13) (200 10 1) simpleGrading (2 2 1) //Block 4
hex (10 9 8 1 21 20 19 12) (200 10 1) simpleGrading (2 2 1) //Block 5
);
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
(
);
// ************************************************************************* //PLOTS:
i. Pressure contour plot
ii. Velocity contour plot
iii. Line plot a distance of 0.085 from x
3. For Grading factor of 0.8
/*--------------------------------*- 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) // Ver 0
(0.08 0 0) // Ver 1
(0.08 0.005 0) // Ver 2
(0 0.005 0) // Ver 3
(0.08 0.01 0) // Ver 4
(0 0.01 0) // Ver 5
(0.2 0.01 0) // Ver 6
(0.2 0.005 0) // Ver 7
(0.2 0 0) // Ver 8
(0.2 -0.01 0) // Ver 9
(0.08 -0.01 0) // Ver 10
(0 0 0.001) // Ver 11
(0.08 0 0.001) // Ver 12
(0.08 0.005 0.001) // Ver 13
(0 0.005 0.001) // Ver 14
(0.08 0.01 0.001) // Ver 15
(0 0.01 0.001) // Ver 16
(0.2 0.01 0.001) // Ver 17
(0.2 0.005 0.001) // Ver 18
(0.2 0 0.001) // Ver 19
(0.2 -0.01 0.001) // Ver 20
(0.08 -0.01 0.001) // Ver 21
);
blocks
(
hex (0 1 2 3 11 12 13 14) (130 10 1) simpleGrading (1 1.25 1) //Block 1
hex (3 2 4 5 14 13 15 16) (130 10 1) simpleGrading (1 0.8 1) //Block 2
hex (2 7 6 4 13 18 17 15) (200 10 1) simpleGrading (1.25 0.8 1) //Block 3
hex (1 8 7 2 12 19 18 13) (200 10 1) simpleGrading (1.25 1.25 1) //Block 4
hex (10 9 8 1 21 20 19 12) (200 10 1) simpleGrading (1.25 1.25 1) //Block 5
);
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
(
);
// ************************************************************************* //PLOTS :
i. Pressure Contours plot
ii. Velocity Contours plot
iii. Line plot a distance of 0.085 from x
Conclusion :
- Changing the grading factordoesnt have a significant impact on the results.
- Maximum velocity in all cases falls in a certain range.
- Maximum velocity for grading factor 0.2 is 2.59, for 0.8 is 2.60 and for 0.8 is 2.62 m/s.
- Velocity contour has less noticable variations.
- looks like solution is near convergence.