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Same results with different thermophysical properties

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Old   April 8, 2014, 16:20
Default Same results with different thermophysical properties
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Lorenzo Gomes
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Hi foamers,

My case is a heatsink subject to natural convection. I'm using chtmultiregionfoam and
I'm trying to make some changes in the thermophysical properties( the kappa value especific) but the results of the simulation are the same no matter whatever the values of kappa I use.

Quote:
thermoType
{
type heSolidThermo;
mixture pureMixture;
transport constIso;
thermo hConst;
equationOfState rhoConst;
specie specie;
energy sensibleEnthalpy;
}

mixture
{
specie
{
nMoles 1;
molWeight 27;
}

transport
{
kappa 209;

}

thermodynamics
{
Hf 0;
Cp 900;
}

equationOfState
{
rho 2700;
}
}

// ************************************************** *********************** //
Any ideias why ?
Thanks.
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Old   April 11, 2014, 14:09
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Thomas Walsh
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can you post pictures of your results and what the different kappa values are that you used?
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Old   April 12, 2014, 22:54
Default boundary condition issue
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Thomas Walsh
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Lorenzo,

I've been playing around with the new OpenFOAM version 2.3.0. I've attached a simple chtMultiRegionSimpleFoam case I made with two different materials (regions). It is a 2D case (front and rear B.C. are empty) with a piece of steel on top of a piece of aluminum. I've applied a constant temperature of 373 K (100 C) to the top surface of the steel and assigned a convective B.C. to the bottom or the aluminum with swak4Foam (see .../0/T for how I did this), so you will need to compile that to get this working. As I'm typing this I'm remembering that I assigned the thermophysical properties required for this boundary condition within it's definition because I was previously using lapacianFoam which you only need to specify the thermal diffusivity [DT]. So I'm basically specify 'rho', 'kappa', and 'Cp' twice, which could be bad for different simulations. I'll have to correct that next time. Does anyone know how I should be specifying these values for the convective B.C.? What if this boundary was split later on into different regions with varying properties?

Just run the Allrun or Allrun-parallel file to start the simulation and use "paraFoam -builtin" to see the results of both regions together. For this case the varying thermophysical properties produced the results that I expected based on a simple thermal resistor equation. I have a feeling that you might not be implementing your B.C. correctly and this is why varying kappa isn't having any effect on the results.

Also attached are the results. Notice at the region connection point (1/2 the height) the slight discontinuity. It appears that openFoam handles the region to region B.C. as a baffle. The results are correct but maybe I should grade the mesh spacing finer towards that transition. Not sure, I'll try some more complex geometries next. Fun Fun Fun!

Thanks,
Tom
Attached Images
File Type: png result.png (27.1 KB, 8 views)
File Type: png resultGraph.png (9.1 KB, 9 views)
Attached Files
File Type: gz conductionTest2b.tar.gz (39.9 KB, 9 views)
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Old   August 13, 2014, 09:28
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Lorenzo Gomes
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Thanks for the replies I stayed a long time without working on this but now Iḿ back, I will see what did you do and look over my code again.
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