BlockMesh Drill down challenge
Objective: To find the change in Velocity magnitude profile with respect to simple grading for a choosen geometry.
Geometry:
Mesh specification
- Number of cells along the x direction (longer dimension) = 200
- Number of cells along the y direction = 10
- Use a graded mesh. Grading factor near all walls should be 0.2, 0.5, 0.8 in each case respectively.
OpenFoam Code to create the above gemetry and meshing
blockMeshDict
/*--------------------------------*- C++ -*----------------------------------*
========= |
\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\ / O peration | Website: https://openfoam.org
\ / A nd | Version: 8
\/ M anipulation |
*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
convertToMeters 1;
vertices
(
(0 0 0) //vertex 1
(0.08 0 0) //vertex 2
(0.08 0.005 0) //vertex 3
(0 0.005 0) //vertex 4
(0.08 0.01 0) //vertex 5
(0 0.01 0) //vertex 6
(0.2 0.01 0) //vertex 7
(0.2 0.005 0) //vertex 8
(0.2 0 0) //vertex 9
(0.2 -0.01 0) //vertex 10
(0.08 -0.01 0) //vertex 11
(0 0 0.03) //vertex 12
(0.08 0 0.03) //vertex 13
(0.08 0.005 0.03) //vertex 14
(0 0.005 0.03) //vertex 15
(0.08 0.01 0.03) //vertex 16
(0 0.01 0.03) //vertex 17
(0.2 0.01 0.03) //vertex 18
(0.2 0.005 0.03) //vertex 19
(0.2 0 0.03) //vertex 20
(0.2 -0.01 0.03) //vertex 21
(0.08 -0.01 0.03) //vertex 21
);
blocks
(
hex (0 1 2 3 11 12 13 14) (200 10 1) simpleGrading (1 5 1) //block 0
hex (3 2 4 5 14 13 15 16) (200 10 1) simpleGrading (1 0.5 1) //block 1
hex (2 7 6 4 13 18 17 15) (200 10 1) simpleGrading (1 0.5 1) //block 2
hex (1 8 7 2 12 19 18 13) (200 10 1) simpleGrading (1 5 1) //block 3
hex (10 9 8 1 21 20 19 12) (200 10 1) simpleGrading (1 5 1) //block 4
);
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)
);
}
TopandBottomfaces
{
type wall;
faces
(
(5 4 15 16)
(4 6 17 15)
(0 11 12 1)
(10 21 20 9)
(1 12 21 10)
);
}
frontAndBack
{
type empty;
faces
(
(0 1 2 3)
(3 2 4 5)
(4 2 7 6)
(2 1 8 7)
(1 10 9 8)
(14 13 12 11)
(14 16 15 13)
(13 15 17 18)
(12 13 18 19)
(21 12 19 20)
);
}
);
mergePatchPairs
(
);
// ************************************************************************* //
The above geomtry is with 0.2 simple grading
OpenFoam code for solver setup
transportProperties - to set kinematic viscosity of chosen fluid
/*--------------------------------*- C++ -*----------------------------------*
========= |
\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\ / O peration | Website: https://openfoam.org
\ / A nd | Version: 8
\/ M anipulation |
*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "constant";
object transportProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
nu [0 2 -1 0 0 0 0] 1e-6; //kinematic viscosity of water at 20C is 1e-6
// ************************************************************************* //To calculate velocity, we know that
`Re =( V*L)/nu`
where `Re` is renolds number
`V` is Velocity of fluid
`L` is characterstic length of domain
`nu` is Kinematic viscosity of water
Let us assume the flow is laminar, then
`Re = 2100 ; L = 0.2 ; nu = 1e-6`
`V = (2100 * 1e-6)/0.2 = 0.0105m/s`
End time = 100sec
dt = 0.001
p - to set pressure
/*--------------------------------*- C++ -*----------------------------------*
========= |
\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\ / O peration | Website: https://openfoam.org
\ / A nd | Version: 8
\/ 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;
}
TopandBottomfaces
{
type zeroGradient;
}
frontAndBack
{
type empty;
}
}
// ************************************************************************* //U - to set initial velocity
/*--------------------------------*- C++ -*----------------------------------*
========= |
\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\ / O peration | Website: https://openfoam.org
\ / A nd | Version: 8
\/ 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 (0.0105 0 0);
}
outlet
{
type zeroGradient;
}
TopandBottomfaces
{
type noSlip;
}
frontAndBack
{
type empty;
}
}
// ************************************************************************* //controlDict - to set end time & dt
/*--------------------------------*- C++ -*----------------------------------*
========= |
\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\ / O peration | Website: https://openfoam.org
\ / A nd | Version: 8
\/ M anipulation |
*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
application icoFoam;
startFrom startTime;
startTime 0;
stopAt endTime;
endTime 100;
deltaT 0.001;
writeControl timeStep;
writeInterval 500;
purgeWrite 0;
writeFormat ascii;
writePrecision 6;
writeCompression off;
timeFormat general;
timePrecision 6;
runTimeModifiable true;
// ************************************************************************* //Output:
The above video shows the flow of fluid in the domain
Line over plot @ 0.2 simple grading
Line over plot @ 0.5 simple grading
Line over plot @ 0.8 simple grading
Plot 1 , 3 , 5 represent the line over plot at points 0.075(before step region), 0.085(after step region), 0.19(at end)
Plot 2, 4, 6 shows the contour plots of velocity magnitude of fluid in the domain
Conclusion
From contour plots, we can observe that as simple grading is increasing (i.e 0.2,0.5,0.8) the velocity is increasing at the step region.
From line over plots, we can observe that as simple grading is increasing (i.e 0.2,0.5,0.8) the velocity magnitude curve at a distance is becoming more smoother( decrease in sharp edges) respectively.