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jose_rodrig June 16, 2011 20:57

Reacting mixtures viscosity

Does anyone know how OF computes the dynamic viscosity of a reacting mixture for the transport equations?

Wonder why OF doesn't ask for an input file with the transport properties like 'transportProperties' as for perfect gas solvers like pisoFoam, etc


novyno June 17, 2011 02:02

Hi Josť,

reactingMixture (is derives from multiComponentMixture) is based on a list of thermophysical data (one for each species) for cp, h, S and viscosity. These data are read from dictionary (i.e. in reactingFoam tutorial, in thermophysicalProperties dict one can find the exact location of the thermo data file). Actually (based on my knowledge...) reactingMixture is templated with sutherland model for viscosity. Finally the general behavior of an OpenFOAM mixture (based on my knowledge...) is to define mu_mixture = sum(y_i * mu_i), where y_ i is the mass fraction.



jose_rodrig June 17, 2011 05:20

Ciau Valerio

Thank you for ur Hint. Can you further point me to the peace of code in the Doxygen docs where mu_mixtures is computed? I was looking for it and I couldnt find.

In fact, for sutherland viscosity model, one needs to parameters, As and Ts, which are the Sutherland parameters and are different for each specie. Also, I am aware of the file thermo.dat that contains the janaf coefficients to compute cp. Are those sutherland coefficient in this same file?

Thx again

novyno June 18, 2011 14:51

Hi Josť,

have a look on


in particular the cellMixture function. Here thermophysical model of the mixture is obtained like a weighted average of the species thermophysical models. So every properties (mu, cp, etc...) are defined in this way (weighted average).

The Sutherland parameters, As and Ts, are the last two coefficients for each species in thermo.dat file. Have a look also to



yashar.afarin June 24, 2011 09:49

Hi Valerio

I have a question about using Sutherland for computing viscosity. I study Yeqn Code in reactingFoam solver and I think that it use only the same muEff for all of the species. I mean that for example the value of muEff for O2 is the same with CH4 one's but if it uses sutherland equation and CHEMKIN (that have As and Ts for each species) they must be different. I am really confused and worried about it.

yashar.afarin June 24, 2011 12:21

Hi valerio

In my "Thermo.dat" file that I get from reactingFoam (and also dieselFoam) tutorial, there are only 19 number for each species. I can't find sutherland coefficents it this file. could you please send me or attach your "Thermo.dat" file?

my email:

Best regards;

yashar.afarin June 24, 2011 12:42


"muEff" is mixture effective viscosity or it is define for each species, at reactingFoam solver-Yeqn?

yashar.afarin June 25, 2011 04:57

Hi Foamers

I found the reason. The value of "muEff" must be equal for all of species. because "muEff=mu+mut" and sutherland coefficient for all of species are the same(for computing "mu"). On the other hand "mut" relates to flow field propertied so is equal for all of species too.

ziemowitzima April 13, 2014 11:20

How viscoisity of the mixture is calculated ?
Dear Foamers,

How is in OF the viscosity of the mixture calculated ?
Is it just linear superposition ? If yes then it seems to be wrong...

Where is it defined/calculated in the source code ?

best and thanks


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