UDF to Define Temperature Dependent Negative Heat Source
 

Hi,

I am trying to calculate the average temperature of interface at each iteration (since I am solving steady state problem) and based on the interface temperature I want to update my negative heat source value (Q_Source=(-constant*(T_Interface-T_Constant))/volume). First, I tried UDM to store interface temperature but didn't work. Then I tried to GLOBAL variable to avoid UDM, but again no luck. I am using ANSYS FLUENT 2019 R2. For both cases, I Interpreted the UDF and during the interpretetion, FLUENT didn't show any error. I have attached my written UDF below. Can someone please help me to fix the problem?

Thanks in advance.

/*********UDF with UDM**********/

#include "udf.h"

/*********INTERFACE TEMPERATURE**************/

DEFINE_EXECUTE_AT_END(average_interface_temp_of_wi ndings_air)
{
Domain *d;
face_t f;
real temper = 0.0;
real A[ND_ND];
real tsavg=0.0;
real area = 0.0;
real area_tot = 0.0;
int ID = 10; /*this is the ID of the interface that I want to get the temperature from*/
Thread *t;
d = Get_Domain(1);
t = Lookup_Thread(d,ID);

/*We are trying to calculate area weighted average temperature of a surface- as per the definition of area weighted average*/

begin_f_loop(f,t)
{
F_AREA(A,f,t); /*get face area which is a vector*/
area = NV_MAG(A);/*get magnitude of the face area*/
area_tot += area; /*calculate total area*/
temper = F_T(f,t); /*calculate face temperature*/
tsavg += temper*area;
}
end_f_loop(f,t)
tsavg /= area_tot;
printf("Average Interface Temperature = %g\n",tsavg);

begin_f_loop(f,t)
{
F_UDMI(f,t,0) = tsavg; /* User Define Memory */
}
end_f_loop(f,t)

}

/**********NEGATIVE HEAT SOURCE***************/

DEFINE_SOURCE(negative_heat_source,c,t,dS,eqn)
{
real source;
face_t f;
source = -5000.*(F_UDMI(f,t,0)-290.); /* For the time being, I have assumed an arbitrary constant for hA and T_Sat */
dS[eqn] = 0.; /* Need to double check. It can be -5000. as a resultant of the derivative of source term */
return source;
}

/******UDF with Global Variable***********/

#include "udf.h"

/*********INTERFACE TEMPERATURE**************/

real tsavg=0; /* Defining Global Variable */
DEFINE_EXECUTE_AT_END(average_interface_temp)
{
Domain *d;
face_t f;
/*real tsavg=0;*/
real temper = 0.0;
real A[ND_ND];
real area = 0.0;
real area_tot = 0.0;
int ID = 10; /*this is the ID of the interface that I want to get the temperature from*/
Thread *t;
d = Get_Domain(1);
t = Lookup_Thread(d,ID);

/*We are trying to calculate area weighted average temperature of a surface- as per the definition of area weighted average*/

begin_f_loop(f,t)
{
F_AREA(A,f,t); /*get face area which is a vector*/
area = NV_MAG(A);/*get magnitude of the face area*/
area_tot += area; /*calculate total area*/
temper = F_T(f,t); /*calculate face temperature*/
tsavg += temper*area;
}
end_f_loop(f,t)
tsavg /= area_tot;
printf("Average Interface Temperature = %g\n",tsavg);
}

/**********NEGATIVE HEAT SOURCE***************/

DEFINE_SOURCE(heat_source,c,t,dS,eqn)
{
real source;
source = -5000.*(tsavg-300.); /* For the time being, I have assumed an arbitrary constant for hA and T_Sat */
dS[eqn] = 0.; /* Need to double check. It can be -5000. as a resultant of the derivative of source term */
return source;
}

if you are using 2019R2 -> it means you run your code in parallel, but it was not considered

you have to modify your code:
Ansys Fluent Customization manual
-> Global Reduction Macros

other problem
in F_UDMI(f,t,0) f is not defined cause you dont have any loops through faces. Define_source has a build in loop over cells


fix these issues first

best regards