[anuarun]

Dear friends,
Below is an excerpt from Fluent manual.

"The UDF must return the real value of the specific heat, and set the sensible enthalpy to the value
referenced by the real pointer h. The entropy is calculated by Fluent as
S=Cp(Tmean)*log(T/Tref)
, where
Cp
is computed by the UDF at
Tmean, the logarithmic average of T and Tref".
2.3.31.3. Example
/************************************************** ********************
UDF that computes specific heat and sets the sensible enthalpy
to the referenced value
************************************************** *********************/
#include "udf.h"
DEFINE_SPECIFIC_HEAT(my_user_cp, T, Tref, h, yi)
{
real cp=2000.;
*h = cp*(T-Tref);
return cp;
}
"
This is as per Fluent UDF User Manual. If cp is computed at Tmean, what does "real cp=2000.;" mean? It is as if we are setting Cp at 2000J/(kg.K). I got confused. Since specific heat macro is already called from within a loop, this will automatically set the Cp value at all cells to be 2000J/(kg.K), right? Then what is the meaning of above statement? I do not know whether I am interpreting it wrongly. I have few more doubts. I will list those.
1.How the macro works?
2.What is the definition of h("enthalpy") in fluent? It seems to be different from the text book definition.
3.What is the reference temp to be given?
4.Is it absolutely necessary that the Cp macro must be compiled (so given in manual)? I do not have visual studio to compile. My Cp udf got interpreted nicely but do not know if it works fine inernally.

Sorry for the long message. I could not help it since no details are given in manual. Please direct me friends.

[anuarun]

posted by mistake

[ngonbadipoor@yahoo.com]

Hi
did you find your answers?


Sent from my iPad using CFD Online Forum mobile app

[anuarun]

I did not find answer to these fundamental questions yet, though I managed to solve my actual problem of writing the temperature and property UDFs!

If you know, Please tell me so that I can add it to the knowledge repository