Hi,

I'm trying to write an UDF to set Neumann condtion ( dv/dy = 0 ). So, i tried this ---------- #include "udf.h"

DEFINE_PROFILE(inlet_y_velocity,thread,position) {

face_t f; cell_t c0,c=-1; Thread *t0 = NULL;

begin_f_loop(f, thread)

{ t0 = THREAD_T0(thread); c0 = F_C0(f,thread); F_PROFILE(f,thread,position) = C_V(c0,t0);

end_f_loop(c, thread) } ------- I just set velocity equal to the velocity of the adjacent cell. but that doesnt seem to work. What should i do? The udf compiles, but the derivative is not 0 on the boundary.

Thanks !

You need to look into how Fluent calculates derivatives (green -gaus divergence center based ) and then set the face value on your boundary so that you make sure it will be zero in the cell. You can find that in any CFD text book or the UDF usermanual.