[yannossss]

Hey guys
I've got a little problem about my UDF program to simulate shear flow in Fluent.
I finally managed to write the UDF program but there is a little mistake somewhere and I can't manage to fix it.

So the geometry of my problem is displayed here -> http://i1129.photobucket.com/albums/...inderinbox.jpg

As you can see I want the shear flow to act on the z-axis direction.

My UDF program is written as follows:

#include "udf.h"

DEFINE_PROFILE(yann_x_velocity, thread, position)
{
real x[ND_ND]; /* this will hold the position vector */
real z;
real u0=1.0;
face_t f;

begin_f_loop(f, thread)
{
F_CENTROID(x,f,thread);
z=x[1];
F_PROFILE(f, thread, position) =1.0+20.0*z;
}
end_f_loop(f, thread)
}


Now the problem in Fluent is:

When I plot the X velocity profile following a line created on the z-axis, the graph given is http://i1129.photobucket.com/albums/...annossss/1.jpg but this is not the solution I want.

On another hand when I plot the X velocity profile following a line created on the y-axis, the graph obtained is http://i1129.photobucket.com/albums/...annossss/2.jpg and this is the graph I'd like to get BUT when I plot the X velocity profile following the line created on the z-axis.

I have tried to modify the UDF file but nothing has worked. I'm pretty sure I am very close to the solution but I didn't mange to find and fix the mistake.

So if anyone could give me a little help I would really much apprecite it.

Thanks for your time guys, I hope you got what my problem is.

Yann

[Galileo]

Originally Posted by yannossss

real x[ND_ND]; /* this will hold the position vector */
real z;
real u0=1.0;
face_t f;

begin_f_loop(f, thread)
{
F_CENTROID(x,f,thread);
z=x[1];
F_PROFILE(f, thread, position) =1.0+20.0*z;
}
end_f_loop(f, thread)
}


Yann

What I guess is wrong is z=x[1];
I think it should be z=x[3]; to mean z=zaxis because z=x[1]; means z=x axis.
At the interface, x=0 in your 3D rectangular geometry.

Notice that the velocity is constant meaning the face coordinate is x=0.

The plot direction, I think, should be x=1, z=0, y=0 ie in the x-direction in your yannossss/1.jpg not z=1.

I suppose all those by using my left hand as the box. Thumb=z axis, first finger=y axis,second finger= x axis, based on your Squarecylinderinbox.jpg

Hope am not confusing you ...lol

Please confirm am right or wrong.

[yannossss]

Thank you very much for the reply unfortunately it does not work.

I also think the mistake comes from the line "z=x[1];"

However I made a little mistake on the Squarecylinderinbox.jpg and the right geometry is http://i1129.photobucket.com/albums/...oxmodified.jpg but I don't think it changes the problem.

When I plot the X velocity with the plot direction being as you advised me x=1, y=0 and z=0 following the line created on the z-axis it doen't give anything. I mean nothing is plotted.

When I do the same but following the line created on the y-axis it gives this http://i1129.photobucket.com/albums/...annossss/3.jpg

Hope you're not confused too and still have some ideas in the back of your mind.

[Galileo]

Originally Posted by yannossss

Thank you very much for the reply unfortunately it does not work.

I also think the mistake comes from the line "z=x[1];"

However I made a little mistake on the Squarecylinderinbox.jpg and the right geometry is http://i1129.photobucket.com/albums/...oxmodified.jpg but I don't think it changes the problem.

When I plot the X velocity with the plot direction being as you advised me x=1, y=0 and z=0 following the line created on the z-axis it doen't give anything. I mean nothing is plotted.

When I do the same but following the line created on the y-axis it gives this http://i1129.photobucket.com/albums/...annossss/3.jpg

Hope you're not confused too and still have some ideas in the back of your mind.

I think the system in Fluent is x=x[0],x[1],x[2] and not 1,2,3

so it should be:

real x[ND_ND]; /* this will hold the position vector */
real z;
real u0=1.0;
face_t f;

begin_f_loop(f, thread)
{
F_CENTROID(x,f,thread);
z=x[2];
F_PROFILE(f, thread, position) =1.0+20.0*z;
}
end_f_loop(f, thread)
}


See the file for my understanding of your model. I like to know if it works.
Make sure your axis system is right in Fluent see the x,y,z system and be sure you bind the BC UDF correctly.

[yannossss]

Hey lad I solved my problem.

So the problem was the cartesian system. In fact the udf is written for my mind with the catesian system I always learnt, meaning: with the right hand, thumb pointing the right designng the x-axis, first finger pointing up designing the y-axis and second finger pointing myself designing the z-direction. It is how Gambit is set and Fluent is also set that way.

The problem comes from the reading of the udf file by Fluent. I don't know why but I realised that when Fluent reads the udf file the cartesian system used changes and is defined as: still with your right hand, thumb pointing the right designing the x-axis, first finger pointing in front of you designing the y-axis and second finger pointing up designing the z-axis.

Which means that on the udf file, the "z" is read by Fluent as a "y". So in Gambit I just rotated the whole geometry by 90° around the x-axis and modify the equation in the udf file and now when I plot the x-velocity in the y direction (y direction that was the z before of course) it gives me what I'm looking for.

Tell me if you understood and thank you very much to have replied quickly to my post to help me.

I wish you all the best. Bye bye

[Galileo]

Originally Posted by yannossss

Hey lad I solved my problem.

So the problem was the cartesian system. In fact the udf is written for my mind with the catesian system I always learnt, meaning: with the right hand, thumb pointing the right designng the x-axis, first finger pointing up designing the y-axis and second finger pointing myself designing the z-direction. It is how Gambit is set and Fluent is also set that way.

The problem comes from the reading of the udf file by Fluent. I don't know why but I realised that when Fluent reads the udf file the cartesian system used changes and is defined as: still with your right hand, thumb pointing the right designing the x-axis, first finger pointing in front of you designing the y-axis and second finger pointing up designing the z-axis.

Which means that on the udf file, the "z" is read by Fluent as a "y". So in Gambit I just rotated the whole geometry by 90° around the x-axis and modify the equation in the udf file and now when I plot the x-velocity in the y direction (y direction that was the z before of course) it gives me what I'm looking for.

Tell me if you understood and thank you very much to have replied quickly to my post to help me.

I wish you all the best. Bye bye

Its good to know you have solved your problem. I don't use Gambit. From what you noticed, it is therefore important to see the geometry coordinate system as displayed in Fluent (irrespective of the meshing software).
Good luck to you.