UDF for saving data of a transient simulation at particular locations
 

Hi
I'm quite new to fluent and UDF programming. Could anyone suggest a method to save just pressure and temperature data at a few locations along X-Axis in a *.dat or *.txt files. I want data only at a few locations becausw otherwise the data to be stored will be very high. I also don't have much time to start learning UDF's. So kindly help

Thank you

You need a UDF that executes after every iterarion, I think that DEFINE_ADJUST (http://jullio.pe.kr/fluent6.1/help/html/udf/node55.htm) should fit your needs. In the reference given you have a sample of code that can be of your iterest, I commented in red what can fit your needs:

#include "udf.h"
DEFINE_EXECUTE_AT_END(execute_at_end)
{
Domain *d;
Thread *t;
real sum_diss=0.;
cell_t c;
d = Get_Domain(1); /* mixture domain if multiphase */
thread_loop_c (t,d)/*This loops over all cells in domain*/
{
if (FLUID_THREAD_P(t))
{ begin_c_loop (c,t)
/*Here you should check if the cell is one of the points you want*/
end_c_loop (c,t)
}
}
printf("Volume integral of turbulent dissipation: %g\n", sum_diss); fflush(stdout); }

To extract the variables you want, check http://aerojet.engr.ucdavis.edu/flue...udf/node90.htm. To save them into a file check http://aerojet.engr.ucdavis.edu/flue...df/node260.htm.

Thank You very much. I will try the links you suggested.

Sreeraj Varma

I'm trying to model ma shocktube through transient simulation. So it is single phase modelling only.I have divided the tube into a a mesh of 1mm longitudinal length cells and I want the pressure at the cell bounded by face at 3.2mI tried to write to write the code as you siggested but an error msg(structure reference not implemented) is coming for line 49(if(Fluid_THREAD_P(t))). Could you pls tell me why. and also pls tell me the purpose of FLUID_THREAD_P(t) and fflush(stdout)

#include "udf.h"

DEFINE_INIT(sree_shock_tube_init,d)
{
cell_t c;
Thread *t;
float xc[ND_ND];

thread_loop_c(t,d)
{
begin_c_loop_all(c,t)
{

C_CENTROID(xc,c,t);

if (xc[0] < 3.2 )
{
C_U(c,t) = 0.;
C_V(c,t) = 0.;
C_P(c,t) = 2026500.0;
C_T(c,t) = 300.0;
C_R(c,t) = 23.536;
}

else

{

C_U(c,t) = 0.;
C_V(c,t) = 0.;
C_P(c,t) = 10132.5;
C_T(c,t) = 300.0;
C_R(c,t) = 0.11768;

}

}
end_c_loop_all(c,t)
}
}
DEFINE_EXECUTE_AT_END(exec)
{
Domain *d;
Thread *t;
float xc[ND_ND];
real pres=0.0;
thread_loop_c(t,d)
{
if(FLUID_THREAD_P(t))
{
begin_c_loop_all(c,t)
{
C_CENTROID(xc,c,t);
if(xc[0]==3.1995)
{
pres=C_P(c,t);
}
} }
end_c_loop_all(c,t)
}
}
printf("Pressure at the cells are %g\n",&pres);
fflush(stdout);
}