Week 11 - Simulation of Flow through a pipe in OpenFoam

Flow simulation procedure:

BlockMeshDict file:

FoamFile
{
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
convertToMeters 1 ; 

 vertices 
( 
	(0 0 0)
	(0 9.993908e-03 -3.489950e-04)
	(0 9.993908e-03 3.489950e-04)
	(2.820000e+00 0 0)
	(2.820000e+00 9.993908e-03 -3.489950e-04)
	(2.820000e+00 9.993908e-03 3.489950e-04)
); 
blocks 
( 
	 hex (0 3 4 1 0 3 5 2) (200 20 1) simpleGrading (1 0.1 1)
); 

 edges 
( 
	 arc 1 2 (0 1.000000e-02 0) 
	 arc 4 5 (2.820000e+00 1.000000e-02 0) 

 );
 boundary 
( 

 axis 
{ 
 	 type empty; 
	 faces 
( 
	 (0 3 3 0) 
	 ) ; 
 }

 wall 
{ 
	 type wall; 
	 faces 
 ( 
	 (1 4 5 2) 
	 ) ; 
 }

 inlet 
{ 
	 type patch; 
	 faces 
 ( 
	 (0 1 2 0) 
	 ) ; 
 }

 outlet 
{ 
	 type patch; 
	 faces 
 ( 
	 (3 5 4 3) 
	 ); 
 }

	 front 
 { 
	 type wedge ; 
	 faces 
 ( 
	 (0 3 4 1) 
	 ) ; 
 	 }

	 back 
 { 
	 type wedge ; 
	 faces 
 ( 
	 (0 2 5 3) 
	 ) ; 
 	 }
);
ControlDict file:

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  9
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    format      ascii;
    class       dictionary;
    location    "system";
    object      controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application     icoFoam;

startFrom       startTime;

startTime       5;

stopAt          endTime;

endTime         15;

deltaT          0.05;

writeControl    runTime;

writeInterval   0.1;

purgeWrite      10;

writeFormat     ascii;

writePrecision  6;

writeCompression off;

timeFormat      general;

timePrecision   6;

runTimeModifiable true;


// ************************************************************************* /
Eplaination:
1. open control dict file in system folder (code: gedit controlDict).
2. Assign start time as 5 and end time 15, delta t 0.05.
 
 
p and U files:
p file:
1. Open 0 folder in block_test
(code: cd..
code :cd 0)
2. Open files p file( code: gedit p)
code for p:
 

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  9
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    format      ascii;
    class       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 2 -2 0 0 0 0];

internalField   uniform 0;

boundaryField
{
    outlet
    {
        type            fixedValue;
        value           uniform 0;
    }
    inlet
    {
        type            zeroGradient;
    }
    axis
    {
        type            empty;
    }

    wall
    {
        type            zeroGradient;
    }

    front
    {
        type            wedge;
    }
    back
    {
        type            wedge;
    }
}

// ************************************************************************* 
1. Assign outlet as uinform 0.
2. Inlet and oulet as zerogradient, front and back as wedge.
 
Open file U file( code: gedit U)
/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  9
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    format      ascii;
    class       volVectorField;
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0.0936 0 0);

boundaryField
{
    inlet
    {
        type            fixedValue;
        value           uniform (0.0936 0 0);
    }
    outlet
    {
        type            zeroGradient;
    }
    axis
    {
        type            empty;
    }

    wall
    {
        type            noSlip;
    }

    front
    {
        type            wedge;
    }
    back
    {
        type            wedge;
    }
}

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

Explaination:

1. Assign outlet and fixedwalls as zero gradient.
2. Front and back empty.
3. Inlet as uniform (0.0936 0 0) fixed value, extracted from MATLAB value.

Transient properties as :

1. Open constant foler
2. Open transientProperties file. (code: gedit transientProperties)
3. Give value for nu = 8.91e-7 (Kinematic viscosity of water)

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  9
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    format      ascii;
    class       dictionary;
    location    "constant";
    object      transportProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

nu              [0 2 -1 0 0 0 0] 8.91e-7;


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

Open paraview:

1. Change directory to block_test
2. Run code: checkMesh
3. Run code:icoFoam
4. Run code: paraFoam
5. In paraview click apply.

Results and discussion:

Paraview:

Geometry of wedge:

Blockmesh:

Select options 'surface with edges' and 'solid color'

Geometry velocity profile:

Select option 'U'

Plots generated at different points:

Velocity profile at 0.25

Velocity profile at 0.5

Velocity profile at 1

Velocity profile at 1.5

Velocity profile at entrance length (2.52)

The Analytical velocity profile obtained from the Matlab :

Analytical shear stress graph obtained by MATLAB:

Pressure drop:

Pressure drop graph of fully developed area.

The value of point at 2.52 is 0.002031

The value of point at 2.82 is 4.53e-6

Difference between them is ∇p∇�= 0.002030547,

obtained from the graph,

analytical value of pressure drop ∇p∇� =2.006 in mm.

Conclusion:

At 2.52 units, where the velocity profile reaches its entire development, the hydrodynamic length is determined.
From the input to the outflow, the velocity profile progressively increases. Once the flow has reached its maximum potential, it doesn't change.
The velocity recorded in openfoam and the calculated velocity profile correspond quite well in that the velocity is greatest in the centre and drops parabolically towards the wall.
The graph produced by openfoam closely resembles the mathematical conclusion; the shear stress is 0 in the pipe's centre and rises linearly towards the wall.
For fully developed flow, the maximum velocity and pressure drop value is attained.