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-   -   Squeeze Flow (http://www.cfd-online.com/Forums/fluent-udf/108536-squeeze-flow.html)

mjaisit October 25, 2012 16:41

Squeeze Flow
 
Hi,
I'm attempting to model simple squeeze flow between 2 plates. I have created a simple rectangle in 2D with axisymmetric geometry, but am having problems getting it to run. Below is the geometry for the file with the specified boundary conditions.

[IMG] http://s3.beta.photobucket.com/user/...ryPic.png.html [/IMG]


I was told by customer support that I need to create a udf, define_cg_motion so I am trying to figure this out as I am new to fluent. Below is the udf I made and interpreted into the setup for the top plate.

# include "udf.h"
# include "dynamesh_tools.h"

DEFINE_CG_MOTION(wallmov, dt, vel, omega, time, dtime)
{
Thread *t;
face_t f;
vel[1]=.1;
}

I specified the system as a transient system with a .001sec time step and to run for 50 time steps.
Without the udf I am getting incorrect results and no visible motion of the top plate. When I try to specify the cg_motion for the top wall i am getting the error: Warning incorrect cg motion UDF wallmov on zone 7 (assuming no motion).
If anyone could help, it would be much appreciated because I have been struggling on this for awhile. Also if the problem is nearly clearly defined please let me know.
Thanks in advance!!!

ghost82 October 26, 2012 02:41

Hi,
you have to move your plate in -x direction!
vel[1] is movement in y direction, with vel[0] you will move your plate in x direction; I think you have to specify a negative velocity to move in -x direction; vel[2] is movement in z direction.
Try this:

Code:

# include "udf.h"
# include "dynamesh_tools.h"

DEFINE_CG_MOTION(wallmov, dt, vel, omega, time, dtime)
{
Thread *t;
face_t f;
vel[0]=-0.1;
vel[1] = 0.0;   
vel[2] = 0.0;
}

Very important:
you have to compile this udf, interpreting it will not work with cg motion macro!

mjaisit October 27, 2012 15:13

Thanks so much for the help, I finally got it working!!!

I have one more question that should be simple but i cant find the answer anywhere. After previewing the mesh motion and the two walls converging how do I reset the geometry and mesh to the beginning? I tried to initialize the solution, but that only resets the iterations and time step and not the geometry. So when I try to run it again I get the error of a negative volume.
Thanks again!

ghost82 October 28, 2012 05:14

Quote:

Originally Posted by mjaisit (Post 388862)
Thanks so much for the help, I finally got it working!!!

I have one more question that should be simple but i cant find the answer anywhere. After previewing the mesh motion and the two walls converging how do I reset the geometry and mesh to the beginning? I tried to initialize the solution, but that only resets the iterations and time step and not the geometry. So when I try to run it again I get the error of a negative volume.
Thanks again!


I think that after previewing the motion you cannot reset the position of the plate..I remember I read this somewhere in the past: save cas and dat files before previewing the motion!

rimi April 21, 2015 06:42

bad convergence
 
I'm a beginner in fluent and i'am trying to model a 2d version of squeeze flow between two disks. I made a simple rectangle(1x20) for the geometry in the xy axis and for the boundary conditions I specified the top as a outflow moving, the bottom as an axis , my left as symmetry and the right boundary conditions as velocity inlet (0.01 m/s).First of all I want to know if my geometry is convienient with my model ? Second in the simulation when i put a fine meshing i found a bad results and when i put a large mesh i found a good results and these are illogical .If anyone has any suggestions it would be greatly appreciated.
Thanks all.


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