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-   -   Different diffusivities for species (http://www.cfd-online.com/Forums/openfoam/77132-different-diffusivities-species.html)

G.Maragkos June 14, 2010 12:50

Different diffusivities for species
 
Hello everyone,

I would like your help if possible on a problem i have. I'm a relatively new user of OF and it might seem simple but i am a stuck with it right now.

I set up a problem of two different species (H2, CO) having simple convection/diffusion equations without combustion, just mixing and i wanna have different diffusivities for them. I know i can just make two dimensionedScalar variables (defined in transportProperties file) but i don't want them to be constant. In the two mass fraction equations i have for the two species, diffusivity is defined by (turbulence->alphaEff(), XX) where depending on the thermophysical model you select, alpha() is calculated.

In the thermophysicalProperties file i define the thermophysical properties of the two species as :
fuelA fuelA 1 2.016 14310 117 8.742E-06 0.7; // H2
fuelB fuelB 1 28.011 1046 29773 1.743E-05 0.7; // CO

but both the equations take the viscosity of the first (H2 here).

Is it possible through the (turbulence->alphaEff(), XX) to calculate different diffusivities for the two species by reading the different properties i define? Or if you can suggest some other way to do so?

Thanks a lot in advance,

Giorgos

smehdi609 June 15, 2010 16:33

In a turbulent flow, the diffusivity is calculated from the turbulent Schmidt number. If you want to have different diffusivities you can specify different Schmidt numbers in your transport equations for species mass fractions.


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