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-   -   OpenFoam validation of 3D Poiseuille Solution (http://www.cfd-online.com/Forums/openfoam/96522-openfoam-validation-3d-poiseuille-solution.html)

alinve January 25, 2012 04:59

OpenFoam validation of 3D Poiseuille Solution
 
Dear foamers,
I'm new user of openfoam and I'm trying to run my first case.
I need to validate OpenFoam against Poiseuille analytical solution.
I need to modelling the 3D Poiseuille flow in a pipe due to a pressure drop.
I've build a case test to be used with icoFoam and a case test to be runned with simpleFoam, disabling the turbolence model. Both solver give me the same solution, that differs from the analytical ones.
The shape of velocity along radius has a parabolic profile but velocity is not zero at the wall, as I expected from the analitycal solution. I've got no idea on how to solve the problem.
I've attached the icoFoam case test, have you got an idea about where I get wrong??
Thanks for any suggestion,
Best Regards
Alice

danishdude January 25, 2012 11:36

Your case did not upload succesfully, so we can't review your setup files. Just to be absolutely certain, is your wall velocity truly set to zero in the /0/U file? It should look something like this:

Code:

   
wall
    {
        type            fixedValue;
        value          uniform (0 0 0);
    }


alinve January 27, 2012 07:20

1 Attachment(s)
Sorry it is the first timethat I use this forum.
I imposed zero velocity at the wall , as you can see in U file:



Code:

dimensions      [0 1 -1 0 0 0 0];

internalField  uniform (0 0 0);

boundaryField
{
    inlet     
    {
        type            fixedValue;
        value          uniform (0 0.05 0);
    }

    outlet     
    {
        type          zeroGradient;
    }

    walls   
    {
        type            fixedValue;
    value        uniform (0 0 0);
    }
}

I try to upload the .zip file another time.
Thanks
Alice

stainboy August 14, 2012 11:38

2 Attachment(s)
Hello,

I was simulating 3D Poiseuille flow and I have problem with validation.
I have a cylinder 3.5mm in diameter and 21mm long. I was forcing flow by setting pressure difference between inlet and outlet (6.5Pa).
From the calculations(mu=3.5e-3Pa/s, nu=3.3e-6m^2./s, rho = 1050kg/m^3 - like human blood) I should obtain V_max=6.7cm/s but from simulation I've got 6.3cm/s. I'm little bit frustrated now.

I'm simulating laminar incompressible flow using simpleFoam.

p
Code:

dimensions    [0 2 -2 0 0 0 0];

internalField uniform 0;

boundaryField
{
    wall
        {
                type zeroGradient;
        }
        inlet
        {
                type fixedValue;
                value uniform 6.5;
        }
    outlet
        {
                type fixedValue;
                value uniform 0;
        }
}

U
Code:

dimensions    [0 1 -1 0 0 0 0];

internalField uniform (0 0 0);

boundaryField
{
        wall
        {
                type fixedValue;
                value uniform (0 0 0);
        }
        inlet
        {
            type pressureInletVelocity;
        value uniform (0 0 0);
               
        }
        outlet
        {
                type zeroGradient;
        }
}

I have mesh prepared in enGrid from STL file (attachement)

Does anybody have some suggestions what might be wrong with my simulation?

I was thinking if maybe the lenght of the pipe is too short. How can I put the fan BC on my inlet and outlet to make this geometry infinite?

Thank you very much in advance for any suggestions

danishdude August 14, 2012 15:46

Keep in mind pressure is dynamic pressure in m^2/s^2 (which is actually P/rho). It looks like you are running the wrong Reynolds number because you have not divided your pressure by the density. Check your transportProperties file as well to make sure you have the right viscosity in there.

ogloth August 15, 2012 03:28

Hi,

the length of the pipe is a good candidate.

The mesh could do with a few more iterations to get the boundary layer straightened out -- the outer surface of the prismatic mesh should be smooth. You might also want to try out a polyhedral mesh, because it runs faster and delivers accuracy not far from hex grids.

Cheers,
Oliver

stainboy August 16, 2012 00:09

Thank you very much for suggestions. I've found my mistake. Problem was laying in the pressure. I forgot to multiply it by rho. I wanted to have pressure drop equal to 6.5 Pa, so I should put the pressure in 0/p file equal to 6.5*1050. Now the results are as they should.


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