problems with UDF to set contact angle
 

Hi,
I am using Fluent to simulate a water droplet flowing down a vertical surface. so it's a multiphase flow and I try to use UDF to define the droplet contact angle as follows:

#include "udf.h"
DEFINE_PROFILE(CA_profile,t,i)
{
face_t f;

begin_f_loop_all(f,t)
{
...........
F_PROFILE(f,t,i)=........;
}
end_f_loop_all(f,t)
}

but it didn't seem to be working properly. my question is will the thread pointer in DEFINE_PROFILE be automatically assigned to the bounday face (between water and air) after hooking UDF to contact angle in GUI? or do i need to specify the boundary face thread pointer before looping?

thank you

han