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Running a simple flow through an orifice

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Old   October 4, 2014, 18:07
Default Running a simple flow through an orifice
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Raghav
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I learning OpenFOAM for about a month. I'm trying to run a simple 2D flow through an orifice. I think the problem is similar to the Cavity one in the tutorial. The problem and the mesh that i generated using blockMesh is attached. I'm using icoFoam as the solver. This is the error I get:

Code:
--> FOAM FATAL ERROR: 
Continuity error cannot be removed by adjusting the outflow.
Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow.
Total flux              : 1.78803e-08
Specified mass inflow   : 4.5e-07
Specified mass outflow  : 0
Adjustable mass outflow : 2.32581e-53


    From function adjustPhi(surfaceScalarField&, const volVectorField&,volScalarField&)
    in file cfdTools/general/adjustPhi/adjustPhi.C at line 118.

FOAM exiting


This is the boundary condition for u:

Code:
dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0 0 0);

boundaryField
{
    inlet
    {
        type            fixedValue;
        value           uniform (0.001 0 0);
    }

    outlet
    {
        type            zeroGradient;
    }

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

    master1
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }

    master2
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }

    topAndBottom
    {
        type            empty;
    }
I've given the velocity boundary condition at the outlet as zeroGradient. So I don't know why the continuity equation shouldn't satisfied.

Can someone tell me where I'm making a mistake?
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File Type: jpg mesh.jpg (54.9 KB, 28 views)
File Type: jpg problem.jpg (37.6 KB, 16 views)
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Old   October 4, 2014, 20:26
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Raghav
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I tried tinkering around. I made the mesh very fine and deltaT very low so that the Courant number is very low. When I run it, it solves for a few time steps and the Courant number increases (order of 0.01) then gives out the same mistake again. I figured this could be because the fluid does not reach the outlet. So I gave a initial velocity for the internal flow field same as that of the inlet velocity. The solver seems to run fine, though I'm not sure if I'll the right answer.

Can someone explain physically and computationally whats happening here?

PS: I had attached a wrong image of the problem before. Correct image attached now.
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Old   October 5, 2014, 09:26
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Alexey Matveichev
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Hi,

it'll be easier to answer your question if you post case files. Right now I can only try to guess that you've got problems with boundaries (boundaries near the orifice to be more exact).
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Old   October 6, 2014, 15:29
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Matthew
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Yes, please attach your case.
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Old   October 10, 2014, 12:25
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Tom Fahner
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Although I am guessing here, I think you should actually change the boundary conditions in your p file. For the outlet you should use:

Code:
outlet
{
     type     fixedValue;
     value   uniform 0;
}
In fact your flow looks more like the pitzDaily (1 inlet, 1 outlet) tutorial than the cavity (only walls).

Regards,
Tom
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Old   October 19, 2014, 21:38
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Thanks @tomf, setting the outlet pressure to 0 worked. Thanks!
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incompressible flow, orifice plate

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