[coolyihao]

#include "udf.h"
DEFINE_PROFILE(x_velocity,thread,index)
{
real x[ND_ND];
real y,z;
face_t f;
begin_f_loop(f,thread)
{
F_CENTROID(x,f,thread);
y = x[1];
z = x[1];
F_PROFILE(f,thread,index) = 20. - y*y/(.0745*.0745)*20.;
}
end_f_loop(f,thread)
}

This is the UDF programming for x velocity inlet (3D)..
If i want to write for pressure difference (3D)...what is the programming for that..thanks

[panda]

It's similar to define the pressure (difference) if you want to apply a pressure boundary conditon.

[Chipsgrottel]

Hello,

I have a problem using an UDF to define my parabolic inlet velocity profile.
I would like to make it this shape:
Vx= -0.00094*y*y+-0.00094*z*z+0.67743

I wrote this helped by your program:

#include "udf.h"
DEFINE_PROFILE(x_velocity,thread,index)
{
real x[ND_ND];
real y,z;
face_t f;
begin_f_loop(f,thread)
{
F_CENTROID(x,f,thread);
y = x[1];
z = x[1];
F_PROFILE(f,thread,index) = -0.00094*y*y+-0.00094*z*z+0.67743;
}
end_f_loop(f,thread)
}

But what I got is a constant profile.
Do you see any mistake?

Thank you for your attention.

[Geisel]

Originally Posted by Chipsgrottel

Hello,

I have a problem using an UDF to define my parabolic inlet velocity profile.
I would like to make it this shape:
Vx= -0.00094*y*y+-0.00094*z*z+0.67743

I wrote this helped by your program:

#include "udf.h"
DEFINE_PROFILE(x_velocity,thread,index)
{
real x[ND_ND];
real y,z;
face_t f;
begin_f_loop(f,thread)
{
F_CENTROID(x,f,thread);
y = x[1];
z = x[1];
F_PROFILE(f,thread,index) = -0.00094*y*y+-0.00094*z*z+0.67743;
}
end_f_loop(f,thread)
}

But what I got is a constant profile.
Do you see any mistake?

Thank you for your attention.

x[0] = x
x[1] = y
x[2] = z

Maybe that?

[Chipsgrottel]

Actually I couldn't do it even with your idea so I did something different:

I designed a long duct with the same conditions as my inlet duct and long enough to let the fluid reach a fully developed profile of velocity. Then I saved it by define -> profile -> write and set it up at the inlet.
Finally it worked.

Thank you for your help anyway

C.