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transport properties for species when using OpenFoam

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Old   September 26, 2018, 23:50
Default transport properties for species when using OpenFoam
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TaoChen
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Hello,guys:
I am working on some numerical simulation about combustion using openfoam. In the combustion/tutorials/reactingFoam/RAS/SandiaD_LTS/constant/thermo.compressibleGasGRI file, for each species there are two transport paremeters:
OH
{
specie
{
molWeight 17.00737;
}
thermodynamics
{
Tlow 200;
Thigh 3500;
Tcommon 1000;
highCpCoeffs ( 3.09288767 0.000548429716 1.26505228e-07 -8.79461556e-11 1.17412376e-14 3858.657 4.4766961 );
lowCpCoeffs ( 3.99201543 -0.00240131752 4.61793841e-06 -3.88113333e-09 1.3641147e-12 3615.08056 -0.103925458 );
}
transport
{
As 1.512e-06;
Ts 120;
}
elements
{
O 1;
H 1;
}
}
I am confused by the meanings of transport parameters As and Ts
Are these parameters used in the sutherland's law for calculation of viscosity. But the there parameters I got through Google should be 1.458E-06 and 110.4, which are different with that in the openfoam file.
Is there anyone could help me comprehend this issue?
Are they same or different?
Thanks very much!!
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Old   October 2, 2018, 07:23
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Yann
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Hello !

The "transport" sub-dictionary is indeed related to the transport model you choose to use, and the parameters will depend on the model.
The user guide sums it up pretty well here : https://cfd.direct/openfoam/user-gui...hermophysical/

As you can see, you were right about it: "As" is the Sutherland coefficient and "Ts" is the Sutherland temperature.

The formulation in OpenFOAM is similar to the one available on CFD-online wiki : https://www.cfd-online.com/Wiki/Sutherland%27s_law
Only the coefficients values are different. You can find here a table leading to the default values you've found in the file you're using (see this post for details and other sources)

I've never ran the tutorial you are using, nor reactingFoam, but it's up to you to choose the best coefficients for your case depending on the fluids you are using and the expected temperature range to calculate a correct viscosity.

I hope it helps!
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Old   October 2, 2018, 11:25
Talking The diffusivity for each species
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TaoChen
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Thank you for your reply!
If you used the combustion solvers in Openfoam, I have another question: why the solvers uses the effective viscosity rather than diffusive coefficient for the governing equations for every species in the diffusive term.
I have searched for some post in CFDONLINE, but it turned out that the assumption that the Le number in combustion is equal to 1 is used in Openfoam. But Le is the relationship between the mass diffusive and thermal diffusive lambda, so it's none of viscosity's business. Do you know why this makes sense in Openfoam.
Thank you again and look forward to your answer.
Best regard!
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