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Jet in still air

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Old   March 17, 2005, 06:20
Default Hi, I want to compute a sim
  #1
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Max
Join Date: Mar 2009
Posts: 24
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Hi,
I want to compute a simple jet in still air in order to asses performance of different turbulence models. I have axysimmetric geometry, two coaxial inflows (10 m/s and 1 m/s), external symmetry plane and an ouflow.
My problem is very simple: after few iterations pressure equation diverges.
I have made the following tests:
1 - switched off turbulence (laminar turbulence model selected)
2 - changed timestep size (turbFoam);
3 - changed viscosity (to stabilize solution);
4 - changed the grid
5 - used version 1.1
but in any case after a variable number of iterations pressure equation diverges, continuity error goes to ~1e30 and so on.
I suspect I have made a mistake in grid generation, but I have tryied either with a Gambit grid and blockMesh generated grid. I have attached the blockMeshDict, if you can have a look, I am quite sure I will find the error immediately. Otherwise can you give further test to do to find the problem?
Thanks
Massimiliano


/*---------------------------------------------------------------------------*\
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 1.0.2 |
| \ / A nd | Web: http://www.openfoam.org |
| \/ M anipulation | |
\*---------------------------------------------------------------------------*/

// FoamX Case Dictionary.

FoamFile
{
version 2.0;
format ascii;

root "/home/didomax/OpenFOAM/didomax-1.0.2/run/simpleFoam";
case "h3_owngrid";
instance "constant/polyMesh";
local "";

class dictionary;
object blockMeshDict;
}

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

arguments "/home/didomax/OpenFOAM/didomax-1.0.2/run/simpleFoam/h3_owngrid";

// convertToMeters
convertToMeters 1;

// list of coordinates of block vertices
vertices
(
(0 0 0)
(0.7 0 0)
(0.7 0.0001 0)
(0 0.0001 0)
(0 0 0.004)
(0.7 0 0.004)
(0.7 0.000348623 0.00398478)
(0 0.000348623 0.00398478)
(0 0 0.140)
(0.7 0 0.140)
(0.7 0.0122018 0.1394673)
(0.0 0.0122018 0.1394673)
);

// list of block descriptions
blocks
(
hex (0 1 2 3 4 5 6 7) (100 1 10) simpleGrading (5 1 1)
hex (4 5 6 7 8 9 10 11) (100 1 40) simpleGrading (5 1 5)
);

// list of curved edge descriptions
edges
(
);

// list of patch descriptions
patches
(
patch jet
(
(0 4 7 3)
)
patch coflow
(
(4 8 11 7)
)
patch outflow
(
(1 5 6 2)
(5 9 10 6)
)
symmetryPlane symup
(
(8 9 10 11)
)
symmetryPlane axis
(
(0 1 2 3)
)
empty lateral
(
(0 1 5 4)
(4 5 9 8)
(3 2 6 7)
(7 6 10 11)
)
);

// list of master-slave patch pairs to be merged
mergePatchPairs
(
);


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

--
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Old   March 17, 2005, 06:32
Default Try running both inlets at the
  #2
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Eugene de Villiers
Join Date: Mar 2009
Posts: 725
Rep Power: 12
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Try running both inlets at the same speed. That should tell you whether it is the mesh causing your problem or not.

Otherwise, having a slugflow inlet hitting a wall is generally not a good idea. Similarly, two adjacent jets entering with a large velocity discrepancy and no space between them is not really physical. Remember, you are specifying zeroGradient pressure at the inlet which is patently absurd under such conditions. I suggest you put a profile on the inlet velocities, move the inlets upstream or separate them some distance.
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