Discontinuity in UDF (How does FLUENT handle it?)

adnanakhtar · January 12, 2015, 12:08

I am using a UDF which involves the variation of thermal conductivity with temperature. The UDF file is as follows:
DEFINE_PROPERTY(cell_thermal_conductivity, cell, thread)
{
real keff;
real temp = C_T(cell, thread);

if (temp < 1373)
keff=0.9;
else
keff = 3.19;

return keff;
}

I wanted to find out if close to the temperature 1373, FLUENT tries to make the function continuous?
I have a slight difference in results when I calculate using a code by considering it as a discontinuity and when I calculate using FLUENT.
Please any help in this regard would be deeply appreciated.

upeksa · January 13, 2015, 04:00

Fluent does not do any magic tricks, it will do whatever you program.
You may probably see an oscillation on your results at 1373 K.

January 12, 2015, 12:08	Discontinuity in UDF (How does FLUENT handle it?)	#1
adnanakhtar New Member Adnan Join Date: May 2012 Posts: 18 Rep Power: 13	I am using a UDF which involves the variation of thermal conductivity with temperature. The UDF file is as follows: DEFINE_PROPERTY(cell_thermal_conductivity, cell, thread) { real keff; real temp = C_T(cell, thread); if (temp < 1373) keff=0.9; else keff = 3.19; return keff; } I wanted to find out if close to the temperature 1373, FLUENT tries to make the function continuous? I have a slight difference in results when I calculate using a code by considering it as a discontinuity and when I calculate using FLUENT. Please any help in this regard would be deeply appreciated.

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January 13, 2015, 04:00		#2
upeksa Member Join Date: Jul 2013 Posts: 80 Rep Power: 12	Fluent does not do any magic tricks, it will do whatever you program. You may probably see an oscillation on your results at 1373 K.