Week 8 - BlockMesh Drill down challenge
- AIM
To program and study the Block Mesh Drill down Challenge using OpenFoam having the following criteria met :
- The number of cells along the direction of flow = 200
- The number of cells along the y-direction for each block = 10
- Inlet Velocity is 1 m/sec
- Study velocity magnitude profile change as a function of mesh grading factor. Use factors, 0.2, 0.5,0.8
- Measure the velocity profile at 0.085 m from the inlet of the geometry
- Plot must be a line plot
- Compare velocity magnitude contours near the step region for the above mentioned grading factors.
- INTRODUCTION
2.1 BlockMeshDict Code Edit
Edit the blockmeshdic file with respect to the problem geometry and also update the bounary conditions accordingly. The below program is given for no grade scheme. In case of grade scheme in X axis play with the 1st coordinate and for 0.2 walls play with the second coordinate of simpleGrading. The formula for finding f (Simple Grading Factor) = size of end cell/size of the first cell.
/*--------------------------------*- 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) //Point 0
(.08 0 0) //Point 1
(.08 0.005 0) //Point 2
(0 0.005 0) //Point 3
(.08 .01 0) //Point 4
(0 .01 0) //Point 5
(.2 .01 0) //Point 6
(.2 0.005 0) //Point 7
(.2 0 0) //Point 8
(.2 -.01 0) //Point 9
(.08 -.01 0) //Point 10
(0 0 0.001) //Point 11
(.08 0 0.001) //Point 12
(.08 0.005 0.001) //Point 13
(0 0.005 0.001) //Point 14
(.08 .01 0.001) //Point 15
(0 .01 0.001) //Vertex 16
(.2 .01 0.001) //Point 17
(.2 0.005 0.001) //Point 18
(.2 0 0.001) //Point 19
(.2 -.01 0.001) //Point 20
(.08 -.01 0.001) //Point 21
);
blocks
(
hex (0 1 2 3 11 12 13 14) (200 10 1) simpleGrading (1 1 1)
hex (3 2 4 5 14 13 15 16) (200 10 1) simpleGrading (1 1 1)
hex (2 7 6 4 13 18 17 15) (200 10 1) simpleGrading (1 1 1)
hex (1 8 7 2 12 19 18 13) (200 10 1) simpleGrading (1 1 1)
hex (10 9 8 1 21 20 19 12) (200 10 1) simpleGrading (1 1 1)
);
edges
(
);
boundary
(
inlet
{
type patch;
faces
(
(0 11 14 3)
(3 14 16 5)
);
}
outlet
{
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)
(10 1 8 9)
(1 2 7 8)
(2 4 6 7)
(11 12 13 14)
(14 13 15 16)
(21 20 19 12)
(12 19 18 13)
(13 18 17 15)
);
}
noslipwalls
{
type wall;
faces
(
(5 16 15 4)
(4 15 17 6)
(0 1 12 11)
(10 21 12 1)
(10 9 20 21)
);
}
);
mergePatchPairs
(
);
// ************************************************************************* //2.2 Initial Condition Pressure p Code Edit
The initial condition can be updated by editing the pressure file available in 0 folder.
/*--------------------------------*- 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;
}
frontAndBack
{
type empty;
}
noslipwalls
{
type zeroGradient;
}
}
// ************************************************************************* //2.3 Initial Condition Velocity U Code Edit
The initial condition can be updated by editing the velocity file available in 0 folder.
/*--------------------------------*- 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;
}
frontAndBack
{
type empty;
}
noslipwalls
{
type noSlip;
}
}
// ************************************************************************* //2.4 controlDict Code Edit
The following parameters were changed in the file
DeltaT = 1e-5
EndTime = 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;
location "system";
object controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
application icoFoam;
startFrom startTime;
startTime 0;
stopAt endTime;
endTime 0.2;
deltaT 1e-5;
writeControl timeStep;
writeInterval 100;
purgeWrite 0;
writeFormat ascii;
writePrecision 6;
writeCompression off;
timeFormat general;
timePrecision 6;
runTimeModifiable true;
// ************************************************************************* //- RESULTS AND DISCUSSION
3.1 No Grading Scheme f=1
hex (0 1 2 3 11 12 13 14) (200 10 1) simpleGrading (1 1 1)
hex (3 2 4 5 14 13 15 16) (200 10 1) simpleGrading (1 1 1)
hex (2 7 6 4 13 18 17 15) (200 10 1) simpleGrading (1 1 1)
hex (1 8 7 2 12 19 18 13) (200 10 1) simpleGrading (1 1 1)
hex (10 9 8 1 21 20 19 12) (200 10 1) simpleGrading (1 1 1)
Inference: Without grading factor or simpleGrading factor has been set to (1 1 1) and the solution is obtained. The main reason for introducing grading factor is to refine the mesh at the desired location for accurate solution. As per the problem statement we are concerned about the velocity profile at x = 0.085 from y -0.1 to y +0.1 which is captured for ungraded mesh and its value is approximately 1.1 m/s.
3.2 Grading Scheme f=0.8
Inference: It is clear from the above results for the grading scheme f = 0.8 the following chages in blockMeshDict file has to be done.
hex (0 1 2 3 11 12 13 14) (200 10 1) simpleGrading (0.8 5 1)
hex (3 2 4 5 14 13 15 16) (200 10 1) simpleGrading (0.8 0.2 1)
hex (2 7 6 4 13 18 17 15) (200 10 1) simpleGrading (1.8 0.2 1)
hex (1 8 7 2 12 19 18 13) (200 10 1) simpleGrading (1.8 5 1)
hex (10 9 8 1 21 20 19 12) (200 10 1) simpleGrading (1.8 5 1)
Then in parafoam using line probe tool we plot and analyse the velocity profile at x = 0.085 from y -0.1 to y +0.1 and its approximate value is 1.1 m/s. It is notable that the velocity profile is smoother than f =1.
3.3 Grading Scheme f=0.5
Inference: It is clear from the above results for the grading scheme f = 0.5 the following chages in blockMeshDict file has to be done.
hex (0 1 2 3 11 12 13 14) (200 10 1) simpleGrading (0.5 5 1)
hex (3 2 4 5 14 13 15 16) (200 10 1) simpleGrading (0.5 0.2 1)
hex (2 7 6 4 13 18 17 15) (200 10 1) simpleGrading (1.5 0.2 1)
hex (1 8 7 2 12 19 18 13) (200 10 1) simpleGrading (1.5 5 1)
hex (10 9 8 1 21 20 19 12) (200 10 1) simpleGrading (1.5 5 1)
Then in parafoam using line probe tool we plot and analyse the velocity profile at x = 0.085 from y -0.1 to y +0.1 and its approximate value is 1.1 m/s. It is notable that the velocity profile is smoother than f =0.8.
3.4 Grading Scheme f=0.2
Inference:
It is clear from the above results for the grading scheme f = 0.2 the following chages in blockMeshDict file has to be done.
hex (0 1 2 3 11 12 13 14) (200 10 1) simpleGrading (0.2 5 1)
hex (3 2 4 5 14 13 15 16) (200 10 1) simpleGrading (0.2 0.2 1)
hex (2 7 6 4 13 18 17 15) (200 10 1) simpleGrading (1.2 0.2 1)
hex (1 8 7 2 12 19 18 13) (200 10 1) simpleGrading (1.2 5 1)
hex (10 9 8 1 21 20 19 12) (200 10 1) simpleGrading (1.2 5 1)
Then in parafoam using line probe tool we plot and analyse the velocity profile at x = 0.085 from y -0.1 to y +0.1 and its approximate value is 1.1 m/s. It is notable that by decreasing grading factor the velocity profile becomes smoother and smoother when compared to f =0.5. This is due to increase in number of cells at the center of flow wherin the major velocity chage is prominent. It also quantifies good amount the boundary layer separation in comparison to other higher grading factors.
|
Grading Scheme f |
U Value Approx (m/s) |
|
1 |
1.1 |
|
0.8 |
1.1 |
|
0.5 |
1.1 |
|
0.2 |
1.1 |
- CONCLUSION
The program to study the Block Mesh Drill down Challenge using OpenFoam was developed and executed successfully.