I am trying to use varying velocity along the height (i.e., power law velocity profile along the height). I am using this user defied function, but I am not sure what is wrong in this program. When I try to initialize the solution, it shows divergence has been detected in amg solver.

#include "udf.h"

DEFINE_PROFILE(inlet_x_velocity, thread, position)

{

real x[ND_ND];

real z;

face_t f;

begin_f_loop(f, thread)

{

F_CENTROID(x,f,thread);

z = x[1];

F_PROFILE(f, thread, position) = 7.087 *pow(z,0.11);

}

end_f_loop(f, thread)

}