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Old   November 15, 2011, 08:26
Default Cp for low temperatures
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Does anybody know what is the equivalent of the Janaf model
for low temperatures (e.g. 30K-600K)? I have not been able to
find a solution to this and my OpenFOAM numerical simulation
keeps diverging.
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Old   November 15, 2011, 10:43
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OK, I need to provide more information for my run case.

A figure of the axisymmetric geometry I am trying to solve is attached, with the initial conditions in pressure. We have atmospheric pressure on the left and very low pressure on the right (my Knudsen is in the limits of the applicability of hydrodynamic equations). The solver I use is rhoCentralFoam and the flow is time-dependent.

There are walls everywhere around (besides the symmetry axis), therefore the boundary conditions can not be causing a problem. As far as the mesh is concerned, I have used a variety of discretizations. The checkMesh report for the latest one is shown below:

Mesh stats
points: 175621
internal points: 156484
faces: 2003103
internal faces: 1964833
cells: 991984
boundary patches: 2
point zones: 0
face zones: 1
cell zones: 1

Overall number of cells of each type:
hexahedra: 0
prisms: 0
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 991984
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
symmetry 17850 9197 ok (non-closed singly connected)
walls 20420 10482 ok (non-closed singly connected)

Checking geometry...
Overall domain bounding box (0 0 0) (0.365 0.365 1.1092)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (-1.10723e-16 -7.12684e-16 1.12382e-16) OK.
Max cell openness = 1.75951e-16 OK.
Max aspect ratio = 7.93857 OK.
Minumum face area = 4.67065e-08. Maximum face area = 9.30723e-05. Face area magnitudes OK.
Min volume = 7.85888e-12. Max volume = 2.72908e-07. Total volume = 0.0942634. Cell volumes OK.
Mesh non-orthogonality Max: 61.402 average: 15.9305
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 0.898818 OK.

Mesh OK.

which is the largest I have generated and seems to be nice. I have varied the Co number down to 0.001, without any success.

In an early stage of the simulation (especially if the outlet pressure is 250Pa instead of 2500Pa), the temperature drops significantly, overcoming the limit of applicability for the Janaf tables. It certainly seems realistic (to me) that the temperature drops below 100K in this case.

So, I guess the only thing left is the thermodynamic properties.
Could someone verify at least if I have checked every possibility?
Is there a relatively easy way to incorporate low temperature data in OpenFOAM?
Attached Images
File Type: jpg geometry.jpg (31.7 KB, 13 views)
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