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PaSR: Computation of mean chemical source term

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Old   April 10, 2014, 10:49
Default PaSR: Computation of mean chemical source term
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Hello All,



With the PaSR model, the mean chemical source term, Schem_mean, in the equation for the mean species, Yi_mean, is typically computed with:
Schem_mean = kappa * Schem(Yi*, T*) .
Here Yi_mean is just called Yi (or Y) in OF, kappa is a function which has the same name in OF, and Schem(Yi*, T*) is the chemical source term determined by (a) the chemical reaction mechanism and (b) evaluated at Yi* and T*, which are the species and temperature of fine scale burning structures. Yi* and T* can be computed from the mean values Yi_mean and T_mean through a PSR calculation (usually at constant pressure and adiabatic), which also gives Schem(Yi*, T*). The above also applies, with slight differences, to the energy equation.

Now, if I understand things well, which could not be the case, what reactingFoam computes is:
Schem_mean = kappa * Schem(Yi_mean, T_mean) ,
which is not what the PaSR model (or EDC model) is supposed to do. I came to this conclusion by examining PaSR.C and ODEChemistryModel.C. This is done either with useReactionRate true or false. Could anybody please show me why and how am I wrong?


Any help will be greatly appreciated.


Regards.

Last edited by csefire; April 10, 2014 at 16:33.
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Old   May 16, 2014, 16:34
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Hello All,

I guess I have to answer my question myself. Strictly speaking, as explained above, the PaSR model does the following:
Schem_mean = kappa * Schem(Yi*, T*) .
However, users of the PaSR model (see paper below) approximate this term with
Schem_mean = kappa * Schem(Yi_mean, T_mean) ,
which is what OF solves for.

Hope this helps somebody.

Regards.

PS: This is the paper:
Berglund, M., et al. "Finite rate chemistry large-eddy simulation of self-ignition in supersonic combustion Ramjet." AIAA journal 48.3 (2010): 540-550.
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