[stuntmanmike]

Hi all,

I am currently simulating jet flames using the Eddy Dissipation Model and the Magnussen Soot Model. For propane jets, I used propane as fuel material, soot as soot material, the Propane Oxygen WD 1 reaction as fuel consumption reaction and 36/44 as fuel carbon mass fraction.
For validation I want to compare the soot volume fractions to values I found in several publications for similar cases. As the soot volume fraction is not available in CFD-Post, I wrote an expression to get the soot volume fraction:

Soot Volume Fraction = (Soot Mass Fraction/(1-Soot Mass Fraction))/(2000 [kg/m^3]/Density).

When I plot the Soot Volume Fraction in radial direction the values correspond quite well to the literature values, however away from the flame boundary the values should reduce to 0, according to the values in literature. In my case they are not. I also checked the Soot Mass Fraction, which neither reduces to 0.
Have I entered the wrong expression or the wrong parameters for the soot model? Any help is appreciated!

I attached some screenshots, showing the graph for the volume fraction, as well as a plot of the volume and mass fraction.

[ghorrocks]

I bet you have a recirculation which transports a small amount of soot from the main flame to the sides. If this flame is meant to be in an infinite field (ie no walls nearby) then you have missed one of the key CFD checks - a sensitivity analysis of the proximity of the outer boundary wall.

[stuntmanmike]

Yes, it is meant to be an infinite field (I used open pressure boundaries). So, you say my boundaries may be to close to the flame?
To be honest, I never thought that this could be a problem. Could you explain this a bit more, please? How do I calculate the minimum distance to the boundaries?
Thanks!

[ghorrocks]

If you look at the streamlines I bet you have a big recirculation from the outlet which takes the soot down the sides.

You should generate another model where the external boundary is twice as far away and compare the results. If it makes a significant difference to the results then keep doubling the distance until the difference is small enough that you can live with it.

[lavero]

how do you carry out a combustion calculation that takes soot into account using the mixture fraction soot model in the openFoam code? what parameters should be entered in the radiationpoperties file in the constant folder in the reactingFoam solver?

[ghorrocks]

No idea. But this is the CFX forum so we would not be expected to know anything about OpenFOAM. Try the OpenFOAM forum.