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Soot absorption coefficient in UDF

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Old   May 9, 2012, 14:48
Smile Soot absorption coefficient in UDF
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Lei Chen
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Hi everyone,

I used the UDF macro DEFINE_PROPERTY(name, c,t) to model the absorption coefficient (Alpha) for gas and soot, the absorption coefficient is a function of gas composition and temperature, and the soot's contribution is calculated using the correlation:

Alpha(soot) = 1232.4*C_R(c,t)*C_POLLUT(c,t,4)*(1.0+0.00048*(T-2000.0));

Then the total Absorption coefficent = Alpha(gas)+Alpha(soot);

The UDF works well for the gas absorption coefficient calculation, however, when I use the variable for soot's mass fraction "C_POLLUT(c,t,4)", this variable gives all zero value in the domain, and thus the soot's effect on absorption coefficient cannot be added into the total absorption coefficient.

I checked the soot mass fraction, and it can be seen reasonably in post-processing.

Some information for my case:
*version: FLUENT 12.1.4
*Problem: propane combustion using a UDF for radiation property
*Model used: SST k-omega, DO, user defined WSGG model, EDC, one-step soot formation model

Thank you for your comments and helps!
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Old   March 16, 2013, 09:33
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Lei Chen
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In case you encounter the same problem. This problem has been solved with helps from a great FLUENT engineer. Use variable C_POLLUT(c,t,IT_SOOT_START) instead, which is the soot mass fraction in (kg/kg).
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