[UnclePetors]

I am a new comer to fluent and udf world. I REALLY need your help. I have been trying to modify the pressure at the circular pipe exit using the mass flux. From several trials, I found that the source of error was 'F_FLUX(f,t)' in 12th line. F_FLUX(f,t) is needed to be pre-defined? I want the pressure profile is updated at every time step. Thank you in advance.

1 #include "udf.h"
2 DEFINE_PROFILE(pressure_profile, t, i)
3 {
4 real pressure;
5 real flt = 0.;
6 real density = 1060.;
7 real pref = 13332.2368;
8 real flref = 6.4*10e-6;
9 face_t f;
10 begin_f_loop(f,t)
11 {
12 flt=F_FLUX(f,t)/density;
13 pressure = pref*flt/flref;
14 F_PROFILE(f, t, i) = pressure;
15 }
16 end_f_loop(f,t)
17 }