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compressibleInterFoam phase capturing

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Old   February 12, 2014, 06:38
Default compressibleInterFoam phase capturing
  #1
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Martin Bartonitz
Join Date: Nov 2013
Location: Hamburg, Germany
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Hi Foamers,

i am not totally new to Foam, but new to the compressible part of foam. So here is my case.

Its an bottle with a narrowing and a nozzle. For the initial conditions i have defined two phases (water=red, nitrogen=blue). The water will be pressed out of the bottle due the internal pressure (internal press = 52 bar, outlet press = 1 bar). The first picture shows the geometry in the YZ-plane. The water in modeled as an perfectFluid with R = 1e40, so that it is almost incompressible.

After a few milliseconds of physical calculation time a recirculation zone establishes (thats what i expected). The recirculation zone is shown in the second picture (alpha) and the third picture (u_Z).

At the bottom is the defined outlet with fixed pressure. All the rest is defined as a wall.

It seems that foam is not really consistent with the phases, because in the recirculation zone is no water but nitrogen. So if the nitrogen phase hits the outlet, the velocity rises and in the end foam aborts the simulation due to the maximum number of iterations for T. So thats clear.

How is the nitrogen phase possible? Could it come due to my setFieldsDict? Does foam fill all default faces with the following filedvalues? If so i should just change the default with the field Values.

Quote:
defaultFieldValues
(
volScalarFieldValue alphaWater 0
volScalarFieldValue p_rgh 52e5
volScalarFieldValue p 52e5
volScalarFieldValue T 293.15
);

regions
(
boxToCell
{
box (-0.2 -0.2 -0.1) (0.2 0.2 0.34833);

fieldValues
(
volScalarFieldValue alphaWater 1
volScalarFieldValue p_rgh 52e5
volScalarFieldValue p 52e5
volScalarFieldValue T 293.15
);
}
);
I have done an investigation with a straight pipe and exactly the same boundarys. That calculations worked just fine (no recirculation area) and i made good results.

Does anybody have an idea?

Best regards

Martin
Attached Images
File Type: jpg overview.jpg (37.8 KB, 10 views)
File Type: jpg backflow_alpha.jpg (45.2 KB, 10 views)
File Type: jpg backflow_uz.jpg (74.2 KB, 11 views)
File Type: jpg jet.jpg (56.0 KB, 11 views)
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Old   February 12, 2014, 07:05
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I would guess its a problem of your dynamic pressure.

The alpha also gets to negative values!?

Maybe you get some strange pressure settings, that lead to something like vacuum.

If you would post some information over your \0 files we could say more. Also a checkMesh would be helpful.
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Old   February 12, 2014, 07:16
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Martin Bartonitz
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Hi pingat,

here is the checkMesh output:

Quote:
Create time

Create polyMesh for time = 0

Time = 0

Mesh stats
points: 621324
faces: 1836959
internal faces: 1810693
cells: 607942
faces per cell: 6
boundary patches: 2
point zones: 0
face zones: 1
cell zones: 1

Overall number of cells of each type:
hexahedra: 607942
prisms: 0
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 0
polyhedra: 0

Checking topology...
Boundary definition OK.
Cell to face addressing OK.
Point usage OK.
Upper triangular ordering OK.
Face vertices OK.
Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
Patch Faces Points Surface topology
OUTLET 3086 3138 ok (non-closed singly connected)
CYL 23180 23232 ok (non-closed singly connected)

Checking geometry...
Overall domain bounding box (-0.0550002 -0.0549702 -0.08) (0.0550002 0.0549702 0.459)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (-1.61615e-15 2.57493e-16 2.21697e-16) OK.
Max cell openness = 3.25416e-16 OK.
Max aspect ratio = 8.32323 OK.
Minimum face area = 1.52359e-07. Maximum face area = 1.98785e-05. Face area magnitudes OK.
Min volume = 1.7119e-10. Max volume = 2.6386e-08. Total volume = 0.00404693. Cell volumes OK.
Mesh non-orthogonality Max: 44.6657 average: 10.857
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 1.07194 OK.
Coupled point location match (average 0) OK.

Mesh OK.

End
Here are the state files from =/

U:
Quote:
dimensions [0 1 -1 0 0 0 0];

internalField uniform (0 0 0);

boundaryField
{
OUTLET
{
type zeroGradient;
value uniform (0 0 0);
}

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

defaultFaces
{
type empty;
}
}
p.org:
Quote:
dimensions [1 -1 -2 0 0 0 0];

internalField uniform 52e5;

boundaryField
{
OUTLET
{
type totalPressure;
value uniform 1e5;
gamma 1;
p0 1e5;
}

CYL
{
type calculated;
value uniform 1e5;
}

defaultFaces
{
type empty;
}
}
p_rgh.org:
Quote:
dimensions [1 -1 -2 0 0 0 0];

internalField uniform 52e5;

boundaryField
{
OUTLET
{
type totalPressure;
value uniform 1e5;//745909.451228;
gamma 1;
p0 1e5;
}

CYL
{
type fixedFluxPressure;
}

defaultFaces
{
type empty;
}
}
T.org:
Quote:
dimensions [0 0 0 1 0 0 0];

internalField uniform 293.15;

boundaryField
{
OUTLET
{
type zeroGradient;
}

CYL
{
type zeroGradient;
}

defaultFaces
{
type empty;
}
}
alphaWater.org:
Quote:
dimensions [0 0 0 0 0 0 0];

internalField uniform 0;

boundaryField
{
OUTLET
{
type zeroGradient;
}

CYL
{
type constantAlphaContactAngle;
theta0 45;
limit gradient;
value uniform 0;
}

defaultFaces
{
type fixedValue;
value 1;
}
}
I guess mut, omega, k are not that important to the problem. Its the foam version 2.2.2

Alpha doesn't get "real" negativ values, more like: Min(alpha1) = -3.83397e-22 Min(alpha2) = -4.26326e-14

Best regards

Last edited by mabar; February 12, 2014 at 08:21.
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