Challenge

Week 8 - Simulation of a backward facing step in OpenFOAM

SSkill-Lync learner23 Dec 2022

Aim:-

To perform the Simulation of a backward facing step in OpenFOAM at (GF=1) and also comparing the results with the grading factor (GF=0.2)

Case 01:- Simulation using the GF=1(simple grading)

BlockMeshDict File:-

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

convertToMeters 0.01;

vertices
(
(0 0 0)
(8 0 0)
(8 1 0)
(0 1 0)
(8 2 0)
(0 2 0)
(20 2 0)
(20 1 0)
(20 0 0)
(20 -1 0)
(8 -1 0)
(0 0 0.1)
(8 0 0.1)
(8 1 0.1)
(0 1 0.1)
(8 2 0.1)
(0 2 0.1)
(20 2 0.1)
(20 1 0.1)
(20 0 0.1)
(20 -1 0.1)
(8 -1 0.1)
);

blocks
(
hex (0 1 2 3 11 12 13 14) (80 10 1) simpleGrading (1 1 1)
hex (3 2 4 5 14 13 15 16) (80 10 1) simpleGrading (1 1 1)
hex (2 7 6 4 13 18 17 15) (120 10 1) simpleGrading (1 1 1)
hex (1 8 7 2 12 19 18 13) (120 10 1) simpleGrading (1 1 1)
hex (10 9 8 1 21 20 19 12) (120 10 1) simpleGrading (1 1 1)
);

boundary
(
inlet // patch name
{
type patch; // patch type for patch 0
faces
(
(0 11 14 3) // block face in this patch
(3 14 16 5)

);
} // end of 0th patch definition

outlet // patch name
{
type patch; // patch type for patch 1
faces
(
(9 8 19 20)
(8 7 18 19)
(7 6 17 18)

);
}

fixedWalls
{
type wall;
faces
(
(4 5 16 15)
(4 15 17 6)
(0 1 12 11)
(9 20 21 10)
(10 21 12 1)

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

//Front

);
}
);

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

Geometry:-

Mesh:-

controlDict File:-

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

application icoFoam;

startFrom startTime;

startTime 0;

stopAt endTime;

endTime 1.5;

deltaT 0.001;

writeControl timeStep;

writeInterval 20;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression off;

timeFormat general;

timePrecision 6;

runTimeModifiable true;

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

fvSchemes:-

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

ddtSchemes
{
default Euler;
}

gradSchemes
{
default Gauss linear;
grad(p) Gauss linear;
}

divSchemes
{
default none;
div(phi,U) Gauss linear;
}

laplacianSchemes
{
default Gauss linear orthogonal;
}

interpolationSchemes
{
default linear;
}

snGradSchemes
{
default orthogonal;
}

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

fvSolution

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

solvers
{
p
{
solver PCG;
preconditioner DIC;
tolerance 1e-06;
relTol 0.05;
}

pFinal
{
$p;
relTol 0;
}

U
{
solver smoothSolver;
smoother symGaussSeidel;
tolerance 1e-05;
relTol 0;
}
}

PISO
{
nCorrectors 2;
nNonOrthogonalCorrectors 0;
pRefCell 0;
pRefValue 0;
}

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

Pressure File:-

/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 10
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
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;
}

fixedWalls
{
type zeroGradient;
}

frontAndBack
{
type empty;
}
}
// ************************************************************************* //

Velocity_File:-

/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 10
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
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 (0.5 0 0);
}

outlet
{
type zeroGradient;
}
fixedWalls
{
type noSlip;
//value uniform (0 0 0);
}

frontAndBack
{
type empty;
}
}

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

Velocity Magnitude Contour:-

Velocity_Streamlines:-

Pressure Contour:-

Case_02:- GF=0.2:-

BlockMeshDict File:-

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

convertToMeters 0.001;

vertices
(
(0 0 0)
(80 0 0)
(80 10 0)
(0 10 0)
(80 20 0)
(0 20 0)
(200 20 0)
(200 10 0)
(200 0 0)
(200 -10 0)
(80 -10 0)
(0 0 1)
(80 0 1)
(80 10 1)
(0 10 1)
(80 20 1)
(0 20 1)
(200 20 1)
(200 10 1)
(200 0 1)
(200 -10 1)
(80 -10 1)
);

blocks
(
hex (0 1 2 3 11 12 13 14) (80 10 1) simpleGrading (0.2 5 1) //Block1
hex (3 2 4 5 14 13 15 16) (80 10 1) simpleGrading (0.2 0.2 1) //Block2
hex (2 7 6 4 13 18 17 15) (120 10 1) simpleGrading (5 0.2 1) //Block3
hex (1 8 7 2 12 19 18 13) (120 10 1) simpleGrading (5 5 1) //Block4
hex (10 9 8 1 21 20 19 12) (120 20 1) simpleGrading (5 5 1) //Block5
);

boundary
(
inlet // patch name
{
type patch; // patch type for patch 0
faces
(
(0 11 14 3) // block face in this patch
(3 14 16 5)

);
} // end of 0th patch definition

outlet // patch name
{
type patch; // patch type for patch 1
faces
(
(9 8 19 20)
(8 7 18 19)
(7 6 17 18)

);
}

fixedWalls
{
type wall;
faces
(
(4 5 16 15)
(4 15 17 6)
(0 1 12 11)
(9 20 21 10)
(10 21 12 1)

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

//Front

);
}
);

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

Geometry:-

Mesh:-

controlDict File:-

application icoFoam;

startFrom startTime;

startTime 0;

stopAt endTime;

endTime 2;

deltaT 0.001;

writeControl timeStep;

writeInterval 20;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression off;

timeFormat general;

timePrecision 6;

runTimeModifiable true;

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

fvSchemes:-

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

ddtSchemes
{
default Euler;
}

gradSchemes
{
default Gauss linear;
grad(p) Gauss linear;
}

divSchemes
{
default none;
div(phi,U) Gauss linear;
}

laplacianSchemes
{
default Gauss linear orthogonal;
}

interpolationSchemes
{
default linear;
}

snGradSchemes
{
default orthogonal;
}

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

fvSolution:-

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

solvers
{
p
{
solver PCG;
preconditioner DIC;
tolerance 1e-06;
relTol 0.05;
}

pFinal
{
$p;
relTol 0;
}

U
{
solver smoothSolver;
smoother symGaussSeidel;
tolerance 1e-05;
relTol 0;
}
}

PISO
{
nCorrectors 2;
nNonOrthogonalCorrectors 0;
pRefCell 0;
pRefValue 0;
}

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

Pressure File:-

/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 10
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
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;
}

fixedWalls
{
type zeroGradient;
}

frontAndBack
{
type empty;
}
}
// ************************************************************************* //

Velocity_File:-

/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 10
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
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 (0.5 0 0);
}

outlet
{
type zeroGradient;
}
fixedWalls
{
type noSlip;
//value uniform (0 0 0);
}

frontAndBack
{
type empty;
}
}

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

Velocity Magnitude Contour:-

Streamline_velocity:-

Pressure Contour:-

GF=1 GF=0.2

The line is inserted in the geometry at a distance of 0.085 from the intake. The velocity magnitude graphs are obtained from two cases of grading GF=1 & GF=0.2

The graph of velocity magnitude with GF=1 is more smoother than that of the GF=0.2

The GF=0.2 is used at convenient positions to capture the vortices accurately which are creating at the step.

2. Explain why Grading/Growth factor is essential for meshing:-

A high-quality mesh also means that there is an optimal balance between the computational cost and the level of fineness achieved.
A low-quality mesh will not only result in inaccurate simulation results but might even cause the solver to produce an error due to instability. Such instability is typically caused by poor-quality or illegal cells. This is something you want to avoid as much as possible.
Meshes should have a considerable increase in quality and accuracy. This not only leads to better convergence, but also more accurate results from your simulations.
Simple grading is the ratio between the size of the end cell and the size of initial cell.
Specifies the maximum ratio of adjacent mesh edges for transitioning between coarse and fine regions.
A smaller grading factor produces a more uniform mesh.

Conclusion:- The two cases are run on the different grading factor, but the GF=1 shows the more smoother line graph of velocity magnitude as compare to GF=0.2.

Week 8 - Simulation of a backward facing step in OpenFOAM

Ship work like this
in your own course.

Talk to a career counsellor

Ship work like thisin your own course.

Talk to a career counsellor

Ship work like this
in your own course.