Hi, I have to put a velocity profile (fully developed) at the inlet of a 3D case. The profile is like a paraboloid centered at middle of the pipe I know that there is an example in the UDF chapter on FLuent doc but there's no 3D case example (definition of a parabolic profile at inlet):

----------------------------- #include "udf.h"

DEFINE_PROFILE(inlet_x_velocity, thread, position) { real x[ND_ND]; /* this will hold the position vector */ real y; face_t f;

begin_f_loop(f, thread)

{

F_CENTROID(x,f,thread);

y = x[1];

F_PROFILE(f, thread, position) = 20. - y*y/(.0745*.0745)*20.;

} end_f_loop(f, thread) } ----------------------------

I don't know how to change that in 3D with the center of the inlet NOT being at the orgin. ( i know there is a thread about this but my case has a slight difference that the inlet pipe is not centered at the orgin. . Someone could help me?

Ronak Shah

You can do two things:

1. Translate/rotate your domain so that the center of your inlet is the origin of axis system and the z axis has its positive direction going inside your inlet. This way you can use the paraboloid I wrote in the thread you make reference to. This should be the easiest way, but you have to pay attention when you specify gravity components, because if you translate/rotate the domain, gravity might not be aligned with one axis.

2. Look for a Math book about rotations and translations, find equations for these transformations and apply the right translation/rotation to the equation of the paraboloid. Then you have to change the UDF code to use the equation you obtained.

Hi

ap