Week 8 - Simulation of a backward facing step in OpenFOAM
The appropriate solver for the given flow condition is icoFoam. From the tutorials folder of the OpenFoam, the cavity tutorial which uses icoFoam solver is copied to the run folder. The blockMeshDict file is edited as below according to the following configuration.
blockMeshDict file
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v2012 |
| \\ / A nd | Website: www.openfoam.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
scale 1;
vertices
(
(0 0 0)
(0.12 0 0)
(-0.08 0.01 0)
(0 0.01 0)
(0.12 0.01 0)
(-0.08 0.015 0)
(0 0.015 0)
(0.12 0.015 0)
(-0.08 0.02 0)
(0 0.02 0)
(0.12 0.02 0)
(0 0 0.05)
(0.12 0 0.05)
(-0.08 0.01 0.05)
(0 0.01 0.05)
(0.12 0.01 0.05)
(-0.08 0.015 0.05)
(0 0.015 0.05)
(0.12 0.015 0.05)
(-0.08 0.02 0.05)
(0 0.02 0.05)
(0.12 0.02 0.05)
);
blocks
(
hex (0 1 4 3 11 12 15 14) (100 10 1) simpleGrading (1 1 1)
hex (2 3 6 5 13 14 17 16) (100 10 1) simpleGrading (1 1 1)
hex (3 4 7 6 14 15 18 17) (100 10 1) simpleGrading (1 1 1)
hex (5 6 9 8 16 17 20 19) (100 10 1) simpleGrading (1 1 1)
hex (6 7 10 9 17 18 21 20) (100 10 1) simpleGrading (1 1 1)
);
edges
(
);
boundary
(
Inlet
{
type patch;
faces
(
(5 2 13 16)
(8 5 16 19)
);
}
Outlet
{
type patch;
faces
(
(15 12 1 4)
(18 15 4 7)
(21 18 7 10)
);
}
fixedWalls
{
type wall;
faces
(
(8 19 20 9)
(9 20 21 10)
(13 2 3 14)
(3 0 11 14)
(11 0 1 12)
);
}
frontandBack
{
type empty;
faces
(
(0 3 4 1)
(2 5 6 3)
(3 6 7 4)
(5 8 9 6)
(6 9 10 7)
(14 11 12 15)
(16 13 14 17)
(17 14 15 18)
(19 16 17 20)
(20 17 18 21)
);
}
);
mergePatchPairs
(
);
// ************************************************************************* //The fluid through the channel is air and its properties are taken at `27^ 0 C` and 101325 Pa.
Next, the p file is edited as follows
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v2012 |
| \\ / A nd | Website: www.openfoam.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
dimensions [0 2 -2 0 0 0 0];
internalField uniform 86143.46691;
boundaryField
{
Inlet
{
type zeroGradient;
}
Outlet
{
type fixedValue;
value uniform 86143.46691;
}
fixedWalls
{
type zeroGradient;
}
frontAndBack
{
type empty;
}
}
// ************************************************************************* //The U file is edited as follows
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v2012 |
| \\ / A nd | Website: www.openfoam.com |
| \\/ 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 0);
}
Outlet
{
type zeroGradient;
}
fixedWalls
{
type noSlip;
}
frontAndBack
{
type empty;
}
}
// ************************************************************************* //The timestep is chosen such that the Courant number is less than one. The kinematic viscosity of air is updated in the transportProperties file.
The controlDict is edited as follows
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v2012 |
| \\ / A nd | Website: www.openfoam.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
application icoFoam;
startFrom startTime;
startTime 0;
stopAt endTime;
endTime 4;
deltaT 0.0005;
writeControl runTime;
writeInterval 0.25;
purgeWrite 0;
writeFormat ascii;
writePrecision 6;
writeCompression off;
timeFormat general;
timePrecision 6;
runTimeModifiable true;
// ************************************************************************* //
In the first case, grading is not applied. The velocity `(V_x)` at x=0.085 m for the first case is obtained as follows.
In the second case, grading is applied and the blockMeshDict is edited as follows
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v2012 |
| \\ / A nd | Website: www.openfoam.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
scale 1;
vertices
(
(0 0 0)
(0.12 0 0)
(-0.08 0.01 0)
(0 0.01 0)
(0.12 0.01 0)
(-0.08 0.015 0)
(0 0.015 0)
(0.12 0.015 0)
(-0.08 0.02 0)
(0 0.02 0)
(0.12 0.02 0)
(0 0 0.05)
(0.12 0 0.05)
(-0.08 0.01 0.05)
(0 0.01 0.05)
(0.12 0.01 0.05)
(-0.08 0.015 0.05)
(0 0.015 0.05)
(0.12 0.015 0.05)
(-0.08 0.02 0.05)
(0 0.02 0.05)
(0.12 0.02 0.05)
);
blocks
(
hex (0 1 4 3 11 12 15 14) (100 10 1) simpleGrading (5 0.2 1)
hex (2 3 6 5 13 14 17 16) (100 10 1) simpleGrading (0.2 5 1)
hex (3 4 7 6 14 15 18 17) (100 10 1) simpleGrading (5 5 1)
hex (5 6 9 8 16 17 20 19) (100 10 1) simpleGrading (0.2 1 1)
hex (6 7 10 9 17 18 21 20) (100 10 1) simpleGrading (5 1 1)
);
edges
(
);
boundary
(
Inlet
{
type patch;
faces
(
(5 2 13 16)
(8 5 16 19)
);
}
Outlet
{
type patch;
faces
(
(15 12 1 4)
(18 15 4 7)
(21 18 7 10)
);
}
fixedWalls
{
type wall;
faces
(
(8 19 20 9)
(9 20 21 10)
(13 2 3 14)
(3 0 11 14)
(11 0 1 12)
);
}
frontandBack
{
type empty;
faces
(
(0 3 4 1)
(2 5 6 3)
(3 6 7 4)
(5 8 9 6)
(6 9 10 7)
(14 11 12 15)
(16 13 14 17)
(17 14 15 18)
(19 16 17 20)
(20 17 18 21)
);
}
);
mergePatchPairs
(
);
// ************************************************************************* //The timestep is varied to 0.0001 for the second case. The velocity profile obtained in this case is as follows.
