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NormalVector October 10, 2012 15:11

Error: update_absorption_coefficient: CO2 not defined
Hey all,

I'm working on a combustion problem and I'm trying to incorporate thermal radiation, specifically the discrete ordinates (DO) model. After doing some research, I wanted to try out the WSGGM method for specifying absorption coefficients. From what I understand, Fluent grabs values from an internal database.

Well, when I go to initialize the solution (with WSGGM specified), Fluent gives me an error: "update_absorption_coefficient: CO2 not defined". It seems CO2 may be missing from the internal database. What's weird is there is no CO2 in my domain at all...

Is there any way to remedy this situation? Maybe there is a place to define this "update absorption coefficient"?

NormalVector October 10, 2012 16:41

I think I've figured out the problem. According to the Fluent User's Manual in regards to the absorption coefficient,

"FLUENT also allows you to input a composition-dependent absorption coefficient, with the local value of a function of the local mass fractions of water vapor and carbon dioxide. This modeling option can be useful for simulation of radiation in combustion applications. The variable-absorption-coefficient model used by FLUENT is the weighted-sum-of-gray-gases model (WSGGM) described in Section 13.3.8. To activate it, select wsggm-cell-based, wsggm-domain-based, or wsggm-user-specified in the drop-down list to the right of Absorption Coefficient in the Materials panel. The three WSGGM options differ in the method used to compute the path length, as described below.

(Remember that you must first enable the species calculation in order to see the wsggm choices in the list, and CO2 and H2O must be present in the mixture.)"

My reaction doesn't produce CO2 but when I add it into the mixture materials and initialize with a 0 mass fraction of CO2, Fluent allows the initialization.

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